What are the requerment for china visa with me?

I am student,my name is mukbul hossain.already i got a offer letter in riga tec. University in Latvia.but there is no latvian embassy in our bangladesh.so i shall apply for latvian student visa in latvian embassy in china.i have no chines invitation letter.what are the requerment for china visa with me?...please inform me.
Your truly
Md: Mukbul.