inquiring about chinese visa inorder to visit wife who is studying in mainland china

hi
my wife is studying in chengdu,sichuan province and i want to visit her. i want to stay there for around 3 months. So will i get a visa for 3 months from kathmandu or do i have to visit a PSB in chengdu to increase my stay. and what documents do i have to submit inorder to get a visa to meet my wife in chengdu