Hei, if I want a tourist visa in China, do I need a hotel voucher?If so, is one night reservation ok?

Yes, the hotel voucher will be required, one night reservation is not ok if you stay in China for a few days. But sometimes, the hotel voucher won't be required if the visa officer think you won't overstay in China and have enough money to burden your expense in China. You can provide other documents such as bank statement, round-trip flight tickets to enhance the chance of success.