The invention provides a stacking mechanism of a paper cup packaging machine, and belongs to the technical field of packaging equipment. The stacking mechanism of the paper cup packaging machine solves the problem that in the prior art, the paper cup stacking efficiency is low. According to the stacking mechanism of the paper cup packaging machine, the paper cup packaging machine comprises a machine frame; the stacking mechanism comprises a feeding guide rail and a discharging guide rail; conveying belts are arranged on the two sides of the feeding guide rail respectively; a discharging hole is formed in the feeding guide rail; the machine frame is connected with a rotating shaft in a rotating mode; a push rod is connected to the rotating shaft in a sliding mode and is fixedly connected to a tray; a supporting spring is arranged on the push rod; a pressing rod is connected on the machine frame in a sliding mode; a sliding rail is further fixedly connected on the machine frame; a limiting frame is connected on the sliding rail in a sliding mode; limiting plates are hinged to the limiting frame; and a power motor capable of driving the rotating shaft to rotate in a reciprocating mode is arranged on the machine frame. According to the stacking mechanism of the paper cup packaging machine, a plurality of paper cups can be automatically stacked together in a sleeved mode, and the efficiency is high.