I got a 13 days stay conference type invitation letter from my Company

You can apply for a business M type to attend the conference. The needed documents include your passport and copies of all used pages, the application form with a passport-style photo attached, invitation letter from the conference organizer, an invitation letter of a duly authorized unit, business license of your company ( original and copy), bank savings account, and round trip air tickets. After, hand in the application to the embassy of PRC to apply for it. It usually takes 4 working days after you submit the application.