A liquid ammonia supply and recovery system comprising an ammonia -fueled engine and a liquid ammonia supply system, characterised in that it comprises furthermore a liquid ammonia recovery system and a nitrogen purging system; wherein the liquid ammonia supply system comprises a liquid ammonia tank used to store liquid ammonia; a low-pressure pump is disposed in the liquid ammonia tank and connected to a buffer tank through a first supply pipeline; the liquid ammonia is pumped out of the liquid ammonia tank by the low-pressure pump, directed to flow through the first supply pipeline and into the buffer tank, pumped out of the buffer tank by a high-pressure pump, directed to flow through a liquid ammonia heater, a liquid ammonia filter, a main gas valve, at least two supply valves, and a second supply pipeline subsequently, and flows into an ammonia-fueled engine; the liquid ammonia recovery system comprises at least two reflux valves, a liquid ammonia collection tank, a first reflux pipeline, and a second reflux pipeline; the ammonia-fueled engine comprises a liquid ammonia outlet connected to the at least two reflux valves through the first reflux pipeline; one end of the second reflux pipeline is connected to the at least two reflux valves, and the other end of the second reflux pipeline is connected to the liquid ammonia collection tank and the buffer tank through a first valve and a second valve, respectively; the liquid ammonia collection tank and the buffer tank are connected through a third reflux pipeline and a third valve; and the nitrogen purging system comprises a gas-liquid separator, a vent mast, a first purging pipeline and a second purging pipeline; an external purging inlet is disposed on the at least two reflux valves and the at least two reflux valves are connected to the gas-liquid separator and the vent mast (21 through the first purging pipeline and a fourth valve; a top part of the liquid ammonia collection tank is connected to the gas-liquid separator and the vent mast through the second purging pipeline and a fifth valve; and a nitrogen purging inlet is connected to the second supply pipeline. an ammonia -fueled engine and a liquid ammonia supply system, characterised in that it comprises furthermore a liquid ammonia recovery system and a nitrogen purging system; wherein the liquid ammonia supply system comprises a liquid ammonia tank used to store liquid ammonia; a low-pressure pump is disposed in the liquid ammonia tank and connected to a buffer tank through a first supply pipeline; the liquid ammonia is pumped out of the liquid ammonia tank by the low-pressure pump, directed to flow through the first supply pipeline and into the buffer tank, pumped out of the buffer tank by a high-pressure pump, directed to flow through a liquid ammonia heater, a liquid ammonia filter, a main gas valve, at least two supply valves, and a second supply pipeline subsequently, and flows into an ammonia-fueled engine; the liquid ammonia recovery system comprises at least two reflux valves, a liquid ammonia collection tank, a first reflux pipeline, and a second reflux pipeline; the ammonia-fueled engine comprises a liquid ammonia outlet connected to the at least two reflux valves through the first reflux pipeline; one end of the second reflux pipeline is connected to the at least two reflux valves, and the other end of the second reflux pipeline is connected to the liquid ammonia collection tank and the buffer tank through a first valve and a second valve, respectively; the liquid ammonia collection tank and the buffer tank are connected through a third reflux pipeline and a third valve; and the nitrogen purging system comprises a gas-liquid separator, a vent mast, a first purging pipeline and a second purging pipeline; an external purging inlet is disposed on the at least two reflux valves and the at least two reflux valves are connected to the gas-liquid separator and the vent mast (21 through the first purging pipeline and a fourth valve; a top part of the liquid ammonia collection tank is connected to the gas-liquid separator and the vent mast through the second purging pipeline and a fifth valve; and a nitrogen purging inlet is connected to the second supply pipeline.