Is china local government invitation mandatory to get visa in business catagory?

Yes, it's a must. Without official invitation letter, you can't get the M type, according to Chinese embassy. Apart from the invitation letter, you still need to provide original and copy of business license of your company, recent six months bank statement, round-trip air tickets.

Thank you Mr. Jack.
If we get invitation from Shanghai company but we like to visit in Zhuhai fair. So Round trip ticket should be for Zhuhai.
Is it ok for the different between invitation and round trip ticket visiting place?

In the invitation letter, it includes where you go. If you go to Zhuhai, your air tickets should be for Zhuhai. Your air tickets should be in accordance with your itinerary.

Thank you Mr. Jack.
Round trip ticker is confirm final one needed? or print copy is ok?

Jabed, the print copy is ok. By the way, I remember that you can download a E-invitation from the website of Canton Fair. This can be used for the application.

Canton fair E-Invitation is ok for business type applicant instead of government invitation?

I think it's OK. You need to check this with the embassy.

Dear Mr. Jack We visited in China 3 times before in 2007, 2009, 2011. Now want to visit this year in Oct. At present what kinds of documents need to apply for my business M type?

You need to hand in your passport, a copy of the passport, a duly filled-out application form with your color bare-headed photo stuck on it, and an invitation letter from a duly authorized unit.

how can i get the loca invitation letter