The invention discloses a venturi mixer. The venturi mixer comprises an inlet pipe, a throat pipe, a shrinking pipe and an outlet pipe which are connected sequentially; the pipe wall of the outlet pipe is communicated with a fertilizer inlet pipe; the inner diameter of the outlet of the inlet pipe is less than the inner diameter of the inlet; the axis of the outlet and the axis of the inlet are not on the same straight line; the outlet is connected with the throat pipe; a plurality of spiral channels are formed in the inner wall of the shrinking pipe; the outlet pipe is communicated with a tipof the shrinking pipe; and the communicating part of the outlet pipe and the shrinking pipe is a wall surface vertical to the axis of the shrinking pipe. When liquid is at the position of the outletpipe, the pressure is minimal and the speed is highest, 0 pressure, even negative pressure occurs at the position of a fertilizer inlet pipe at the moment, a fertilizer beating pump is started, fertilizer beating is conducted, liquid fertilizer and water flow rotating at high speed are rapidly mixed at the position of the outlet pipe at one moment, the aim of completely mixing fertilizer is fulfilled, and the venturi mixer is uniform in mixing and high in efficiency.