The invention relates to scissors lifting gears, and especially relates to a seat lifting mechanism. The seat lifting mechanism comprises an upper bracket, a lower bracket, a first support bar, a second support bar, an upper sliding block, a lower sliding block and a transmission rod. The transmission rod is fixedly connected to the bottom of the lower bracket, the first support bar and the second support bar are hinged in a center crossing way, the upper end of the first support bar is hinged to the upper bracket, the lower end of the first support bar is hinged to the lower sliding block, the lower sliding block is connected to the lower bracket in a sliding way, the upper end of the second support bar is hinged to the upper sliding block, the lower end of the second support bar is hinged to the lower bracket, the upper sliding block is connected to the upper bracket in a sliding way, the lower sliding block comprises a lower bracket connection portion and a transmission rod connection portion, the lower bracket connection portion is connected to the lower bracket in a sliding way, the transmission rod is provided with a transmission part, and the transmission part is used for connecting the transmission rod connection portion to the transmission rod in a sliding way. The accurate vertical adjustment can be guaranteed, the lifting height range is great, and the reliable stiffness and bearing capacity are guaranteed.