I think the key is to demonstrate your parents' strong ties to China. The following documents help: - their income situation: salary, income, etc. - your siblings' situation; - your parent's properties, and other information about their financial status. The key is to show that they are inclined to return after a short visit. It would be good to write a short letter of invitation. Summarize the visiting plan and intention of returning. Different from immigrant visas, when applying for a visitor visa, the VOs first assume that the applicants intend to immigrate, then use evidence to help them eliminate that assumption. I guess nobody knows exactly how a case is reviewed. When my parents applied, the VO hardly looked at anything they submitted, and approved within a couple of minutes after one or two easy questions. We made sure that my parents didn't overstay their visa, so that to build a good track record.