regarding M visa

Normally speaking, the M type allows you to stay for one month or so. The maximum stay duration allowed by M type would be three months.

What would help me to get the one for 3 months? As iam on a business tour its appreciable if I get the one for 3 months.

You still have the chance to get a three-month stay duration if the invitation letter provided by your partner states the period needed is about three months or so. If the office only gives you one or two month, you can first enter China, and then extend it at the local exit and entry bureau before the M type expires.