The invention discloses a natural gas power ship fuel monitoring system and a fuel monitoring control method and device. The natural gas power ship fuel monitoring system comprises a fuel bin, a first vaporizer, a first mass flowmeter, a first switch valve and a second switch valve. The first vaporizer comprises a first hot flow pass and a first cold flow pass which are mutually isolated. An inlet and an outlet of the first hot flow pass communicate with a heat supply loop of a ship, an inlet of the first cold flow pass is connected with a liquid supply port of the fuel bin, and an outlet of the first cold flow pass is connected with a gas inflow passage of a ship power device. The first mass flowmeter is used for detecting the first mass flow of natural gas entering the ship power device. The first switch valve is connected between the inlet of the first cold flow pass and the liquid supply port of the fuel bin. The second switch valve is connected between the outlet of the first cold flow pass and the gas inflow passageway of the ship power device. Compared with the prior art, through the scheme, real-time accurate monitoring for the ship fuel consumption quantity can be achieved, and economical operation of the ship is facilitated.