A method for prepare snse nanoparticles as a cathode material of a lithium ion battery by a microwave hydrothermal method comprise that following steps: 1) adding 0.0237- 1. 185 part by weight of sodium borohydride into 1- 10 ml deionized water, stirring until completely dissolved to form a transparent solution A, and adding 0.000 part by weight. 2) adding 0. 1 ~ 5.259 parts of sncl4.5h2o into 9 ~ 80 ml ethylene glycol solution, and stirring until it becomes a transparent solution C, and the molar ratio of selenium powder to sncl4.5h2o is1:(1.0 ~ 2); 3) Dropping solution B into transparent solution C, and quickly changing it into black solution D; Placing the solution D on a magnetic stirrer, and stirring at a speed of 400- 1000 rpm for 0.5-6 hours; 4) Pour the solution D into a polytetrafluoroethylene reaction kettle and transfer it to a microwave hydrothermal reactor. The reaction temperature is 120 ~ 180℃ and the reaction time is 0.5 ~ 12h. After the reaction, the solution D was centrifuged to obtain black powder, which was repeatedly washed with anhydrous ethanol and deionized water for 5 times to obtain black snse nanoparticles. Among them, the volume filling rate of PTFE reactor is 10 ~ 90%.