How long can a Chinese citizen visit to the US on a visa ?
What type of visa? Assuming tourist/visit visa since you say "visit," the maximum possible on a tourist visa is 180 days. If you are approved for a visa, immigration at port of entry will specify your time limit within that 180 day maximum, depending on your funds for all typical tourist expenses, date of your scheduled return flight home, tourist plans. You are also limited to a maximum of 180 days in any 365-day period. So if you were to obtain a multiple-entry visa, you are still limited to a maximum of 180 days in the US out of any 365-day period. So you must be out of US at least as long as you were in. Multiple-entry does NOT extend maximum period allowed in US when you enter. It just saves you the trouble of getting another visa during the 5- or 10-year term when the visa is valid. Overstay your visa, and you won't be getting another one (& multiple-entry visas are revoked). You won't get any visas elsewhere, either, since US shares visa, immigration, deportation, & criminal records with practically every country on the planet.
It depends what visa, for what purpose.
It depends what visa the Chinese citizen is in the US on.
That depends on what visa they have