is it possible to apply with one way flight? Also I might stay there not in hotel,but in apartment, is it enough to give apartment address?

You should apply for a M type for your visit to Canton Fair. The round-trip air tickets and hotel booking are required for some nationals like Pakistanis. Some nationals are even required to provide an invitation letter from duly authorized Chinese unit authorized by the Ministry of Foreign Affairs of PRC beside the invitaion letter from the Chinese company. I think you should apply from the Chinese embassy in your country in advance.