on L type visa buying goods

Qudrat, I am afraid that you can't apply for individual L type from Chinese embassy in your country. And you should apply for a M type for your visit. It requires:
1. your passport, filled applicaiton form and a recent passport photo
2. invitation letter from duly authorized Chinese unit. Your Chinese partner company should help you acquire this.
3. translation of your address (in English)
4. your account. It should have at least 4000USD inside.
5. non-criminal record (English version) certified by your Ministry of Foreign Affairs
6. round-trip air tickets