How the woman that have age under 40 years old to get visa to entry to China?

You should apply for a M type with the help of your business partner in PRC. The documents required are:
1. invitation letter from your Chinese business partner.
2. a copy of your business partner's company business license.
3. round-trip air tickets and hotel booking.
4. your itineraries during your stay in PRC.
5. passport, passport photo and filled application form.
6. the embassy might requires that you provide travel insurance, bank statement, employment certificate or any other kind of financial proofs.

After you prepare all required documents, you should submit them to Chinese embassy in your country and wait for their approval.