A new scheme that is able to control the electron injection phase in the plasma wakefield based on the ponderomotive acceleration of electrons is proposed. The scheme uses the far-infrared laser as an injection pulse which copropagates behind the pump laser. Electrons located in the rear of the first period of the wakefield are pre-accelerated by the injection pulse and get injected at the phase that is determined by the distance between the two laser pulses. 1D Hamiltonian analysis and 2D particle-in-cell simulations have been performed to investigate the trapping process, as well as the influence of injection phase on electron energy and beam charge. With the proper injection phase, the maximum injected electron charge that is limited by the beam loading can be achieved.