A paper feeding mechanism includes a mechanical frame, a drive system mounted to the mechanical frame, an input tray pivoted to the mechanical frame, a controlling assembly, a pickup assembly and an elevating assembly. The pickup assembly includes a pickup roller and a pickup wheel pivoted to the pickup roller. The elevating assembly mounted to the mechanical frame is pivoted to the input tray. The controlling assembly includes a controlling system, a paper sensor, a floating sensor, and a pickup sensor detecting a position of the pickup assembly to get a total thickness of papers on the input tray. The controlling system controls the drive system to drive the elevating assembly to wiggle upward and downward to drive the input tray to rise and descend according to the total thickness of the papers on the input tray so as to make the pickup wheel pick up the papers steadily.