The invention relates to a seat lifting device of an infant cart, which is provided with two independent symmetric structures which are arranged a left side front foot pipe and a right side front foot pipe, each independent structure comprises an adjusting seat, an adjusting seat outer cover, a button, a compression spring, a gear iron slice, an adjusting pin and the like, wherein the adjusting seats are sheathed on the front foot pipes, the adjusting seat outer covers are fixed at the adjusting seats, the left adjusting seat and the right adjusting seat are connected through a front fixed pipe and a back fixed pipe, the seat assembly of the cart is held on the front fixed pipe and the back fixed pipe, the weight of a seat can be delivered to the ground from the front ends of the gear iron slices which are inserted in the gear holes of the front foot pipes, fingers push the buttons in the adjusting seats so that the front ends of the gear iron slices are drawn out of the gear holes of the front foot pipes, the seat can move up and down along the front foot pipes, and then, the compression springs push the buttons, and further push the adjusting pins to drive the front ends of the gear iron slices to be inserted in the gear holes of the front foot pipes, i.e. the seat is fixed again after the height of the seat is changed. The device disclosed by the invention eliminates the functional defects in the existing infant cart.