The invention relates to a two-stage diagonal fan, belongs to the diagonal fan type mechanical devices, solves the problem that existing diagonal fans are not high in specific speed and total pressureefficiency, and is applied to a bladeless fan and a pipeline fan. The two-stage diagonal fan provided by the invention comprises an outer shell, a front inner pipe, a front guide blade, a front motor, a back inner pipe, a back guide blade and a back motor, wherein the front motor, a front rotary shaft, a front wheel, a front blade and the front guide blade form a first-stage diagonal fan, and theback motor, a back rotary shaft, a back wheel, a back blade and a back guide blade form a second-stage diagonal fan. The front and back blades are crankled blades, so that the efficiency of the fan can be improved effectively; triangular sawteeth distributed along the spanwise directions of the blades are arranged on the back edges of the blades, so that the noise level of the motor can be reduced. The two-stage diagonal fan provided by the invention can further enhance the wind pressure, can be applied to a tubular structure where a centrifugal fan cannot be used, and can overcome on-way resistance of a pipeline to send out an air flow, so that defects of an axial flow fan without sufficient pressure rise can be overcome, and the two-stage diagonal fan also has obvious advantages in blast capacity compared with that of the centrifugal fan.