can i apply a X visa in chinese embassy in tokyo?

If you have student ID in Japan, you can submit your China visa application to Chinese embassy in Tokyo.

I was a student in china and i came to japan for conference and my x visa has expire which is chinese x visa and i want to go back to china for my studies i talk to my university in china and they have send me documents please i want to know if i can apply from here to china with my jw202 and my admission letter from my former school in china. I study in china not japan

Yes, you can apply for a X visa there providing your entry record for Japan. Or you can apply through a travel agency.