The utility model provides a propping agent flow direction conversion device which is arranged between a sand hopper and a sand-liquid mixing barrel of a sand mixing truck. The propping agent flow direction conversion device comprises propping agent conveying channels and a flow direction conversion baffle, wherein the propping agent conveying channels comprise the sand inlet channel, the sand return channel and the sand outlet channel. The front end of the sand inlet channel is connected with an auger sand outlet opening connected to the sand hopper, and the tail end of the sand inlet channel is connected with the front end of the sand return channel and the front end of the sand outlet channel in parallel. The tail end of the sand return channel corresponds to the sand hopper. The tail end of the sand outlet channel is connected with a sand inlet opening of the sand-liquid mixing barrel. The flow direction conversion baffle is movably arranged at and shields the front end of the sand return channel or the front end of the sand outlet channel, namely, the flow direction conversion baffle closes the sand return channel or the sand outlet channel. The propping agent flow direction conversion device is simple in structure, low in cost and capable of being directly added to an existing sand mixing truck without changing the sand mixing truck. In the impulse type sand fracturing process, the propping agent flow direction conversion device can achieve rapid conversion of the flow direction of propping agents in two seconds, the conversion frequency is high, and forming of columnar propping of the propping agents is facilitated.