Dear respected. I have already invitation from china.

You can make the application from the China embassy.
Address: Sardar Shah Mahmoud Ghazi Watt, Kabul, Afghanistan
If it's a business invitation letter, first, prepare the required documents including copy of passport, the filled-out application form, 2 passport-style photos, your company’s business registration certificate and its copy, non-criminal proof and its English translation, and an invitation letter from a duly authorized unit.
Next, submit the application to China embassy.