The invention discloses a preparation method of a bipolar membrane with high temperature resistance, low electrical resistance and excellent mechanical property. The preparation method comprises the following steps: uniformly modifying conducive particles on the surface of a melt-blown fiber net by ultrasonic dispersing to obtain a high-conductivity fiber net; adding carboxylated multi-wall carbon nanotubes in an SA solution, and carrying out uniform ultrasonic dispersion to obtain modified anode membrane liquid; soaking the conductive fiber net in the anode membrane liquid for 3-5 minutes, taking out the conductive fiber net and marking the conductive fiber net as an m-SA membrane; adding the carboxylated multi-wall carbon nanotubes in CS sol, and carrying out uniform ultrasonic dispersion to obtain modified cathode membrane liquid; soaking the conductive fiber net in the cathode membrane liquid for 3-5 minutes, taking out the conductive fiber net, superposing the conductive fiber net to the m-SA membrane, and drying to obtain the bipolar membrane m-SA/CS. The conductive fiber net is used as a supporting base material to prepare the bipolar membrane, the stability and the mechanical property of the bipolar membrane can be improved, the electrical resistance of the membrane is reduced remarkably, and therefore, the bipolar membrane with high temperature resistance, low electrical resistance and excellent mechanical property can be widely applied to the fields of high temperature environments, water treatment, heavy metal ion recover and the like.