An S valve pump with a buffer function comprises a cylinder, a first main cylinder, a second main cylinder, an S pipe and a compensation cylinder, wherein fluid with solid aggregate is contained in the cylinder; the first main cylinder and the second main cylinder are used for alternately sucking the fluid from the cylinder and alternately discharging the fluid to the S pipe; one end of the S pipe is connected with a middle slurry discharge pipe, and the other end of the S pipe can be in butt joint with the first main cylinder and the second main cylinder alternately; and the compensation cylinder is used for discharging the fluid to an output slurry discharge pipe during intermittent cut-off of the output slurry discharge pipe so that uniform continuous flow can be formed in the output slurry discharge pipe. The S valve pump is simple in structure, and slurry discharge is continuous and uniform.