Chinese law prohibits direct employment by any Chinese airline, all flight crews are employed by an agency.
For tax reasons for the airlines most (probably all) are located in Hongkong. You are employed and paid by the agency. The agency then puts you on a service agreement with the Chinese airline, you are leased back for which the agency gets a fee.
Basically there are two contracts: 1 between you and the agency and 2 service contract between the agency and the airline.
You need to legally dissect the tax agreement:
All tax treaties are based on the OECD model treaty and adapted to the specific situation between the contracting states.
Remember the treaty is not written with the tax payer in mind, but with the tax collector in mind, the title is misleading (as usual...)
Part 1 of all the treaties describes which state CAN collect the tax, it decides which state gets the full 'lute'.
Part 2 describes if the other state can still get some of the tax if the tax is higher than in the first state (preventing double taxation).
Incidentally that gives the outcome for us personally; as where to pay which tax.
First you will have to find out where you are a resident, that depends on art. 4
If you only have a permanent home in your home country, you are a resident there.
If you only have a permanent home in China, you are resident there.
If you have both a permanent home in your home country and China, it depends on where the centre of vital interest is; where your family is, schools, clubs, etc
If you have no permanent home in either, you are a resident where you have your habitual abode (where are you normally spend most of your time)
If all the above is not applicable you are deemed a resident from the State your are a national of.
Permanent home is not a hotel....
For arguments sake lets put it that you are deemed a resident of your home country:
Art. 14/15 would then be as follows:
1. In principle your home country (contracting state) can collect tax on your world income, however if part of that is earned in China (other state), China can tax you on that part.
As a general rule taxes in our home countries are higher than in China, according to art. 23 from the model (different per treaty, for instance UK art. 22)
the home country can then collect the difference between the two.
2. Notwithstanding: even though article 1 gives China the right to collect tax, in case of the following 3 are true, ONLY the home country can collect tax:
a) backward reasoning: you have been less than 183 days in China (more than 183 days in your home country)
AND
b) your are paid by your agency which is in itself NOT a resident of China (they reside in Hongkong)
AND
c) The agency is a separate entity form the airline.
Normally we are more than 183 days in China (or less the 183 days in your home country)
a) is not true...
b) is true
c) might be true depending on your agency
As it was AND for all 3 that means that paragraph 2 is not applicable and both China and your home country may collect tax.
Then art 15 paragraph 3:
Notwithstanding: Even if art 1+2 where applicable, if the employment involves international traffic on aircraft, China (the other state) may collect tax.
Which is the case for us, so China may collect tax as well as your home country.
Mark the difference between the wording in art. 1+3 and art. 2: In art. 2 it explicitly mentions that ONLY the home country can collect tax, in 1+3 the wording is such that BOTH the home country and China can collect tax, in that case you pay full tax in China where that amount is then deducted towards tax owed in your home country.
If your are deemed a China resident it is all very simple, you only pay taxes in China unless you have income in your home country.
So make sure you are seen as a resident of China!
Different treaties have different rules concerning double tax and what you own to whom, but this is the basic, so check your home countries tax agreement with China to see what needs to be payed and do inform yourself with expert councel.