A rotary spray nozzle includes a barrel, a coupling tube set including a coupling tube rotatably supported in axle bearings inside the barrel, a pressure tube connected to one end of the barrel and defining a gas intake passage that is kept in fluid communication with the coupling tube and reduces in direction toward the coupling tube for causing a Venturi effect to pressurize a flow of compressed gas and fluid passing therethrough, and a bent nozzle tube connected to one end of the coupling tube remote from the pressure tube for free rotation with the coupling tube relative to the barrel when the pressurized flow of compressed gas and fluid is passing out.