how can i get multiple visa?

i've visited china before for 7days and visa type was F. now i need to visit china many time within 6 months for my business. I'm a sole agent of a Chinese company. so, for that reason i'm interested to get a multiple visa for 6months to 12 months as if i can visit as many time as i want within the validity.
what do i need to apply for multiple visa or what are the requirement to get multiple visa?
please let me know details.
Thank you