The invention relates to a preparation method of a novel liquid side surface high-resistance layer for increasing the 2ms square wave through flow of a zinc oxide piezoresistor. The method comprises the steps of mixing the prepared raw materials, heating for dissolving to prepare a uniform solution, and directly coating the side surface of a foamed resistance piece with the solution. The method ischaracterized by comprising a raw material preparation step, a ball-mill mixing step, a spray drying step, a compression formation step, a sintering step, a coating step and a piece formation step, wherein the raw material preparation step, the ball-mill mixing step, the spray drying step, the compression formation step, the sintering step and the coating step are sequentially carried out. The preparation method has the beneficial effects that by selecting a formed upper high-resistance layer, the fluctuation, caused due to non-uniform pre-sintering shrinking rate of the thickness in the past, of a glaze layer is reduced, and the process is relatively stable.