i want to know how can i got longer & multiple entry chinese visa ???

i am iranian my waif is chinese and i dont have any longer visa to living with my family in china , i don't have business in china but always i go to china to see my family .........
i living in guangdong shonde foshan lecong , i rent a house , my waif with my baby living there but always i go there to visit them & i have problem for visa :-(
pls help me to resolve this problem.

i have business in iran and before i got one month business visa from china embassy in tehran but now.....

i want to know what i should do to get a longer visa and multiple entry to china ???

i waiting for your kindly replay :-)

tks & regards