This paper studies the dynamic characteristics of combination resonances of a plate partially immersed in fluid with a time-dependent axial speed. Based on the theory of von Kármán large deflection plate and taking into account of the effects of the fluid-structure interaction, the tension force and the time-dependent speed, the nonlinear dynamic equations of the plate partially immersed in fluid are established. By applying the Galerkin method to discretize the equations, the nonlinear dynamic equation set in modal coordinates is then obtained. The effects of parameters such as the average speed, the pulsating speed and the tension force on the nonlinear dynamic characteristics of the system are analyzed through the multiple scale method and the numerical method. It is revealed that when a combination resonance occurs, the system shows a complex dynamic behavior, the amplitude of the first order modal response is far larger than that of the second order, and the influence of the average speed and the pulsating speed on the frequency-response curve is quite remarkable.