There is no requirement to write Chinese before writing English for the postgraduate entrance examination. This mainly depends on your English. If you have confidence in English, you can be recommended to write English first. After all, for China people, English is more difficult than Chinese. Of course, if your English is not good, you should write Chinese first. By the way, I'll tell you a little skill in writing a composition. If you really can't write a composition and the words are poor, then you can extract a few words that you personally think are better from your previous reading comprehension or cloze. This will make your whole composition look much better. It's just a trick I use every time I write an English composition.