Lubrication and sealing are the key research points in water hydraulic technology. A better seal is provided by the structure form of the poppet valve comparing to the spool valve, however, poorer linearity and control accuracy accompanies inevitably. Aiming at improving the control performance of poppet valves, the design of the water hydraulic digital valve is analyzed in this paper. A high speed digital valve is designed and controlled by PWM (Pulse-Width Modulation) and actuated by a piezoelectric ceramic stack with high frequency response and control stiffness. Another new design using poppet valves for digital bits is proposed to ensure enough seal ability and lower the cost of the valve, namely the multi-digit on-off valve. The simulation models of these two types of valves are built and the results show the different performances between the valves. The high speed digital valve is provided with high control accuracy and responsiveness. In contrast, large overshoot and oscillation are encountered during switching on the digits of the multi-digit on-off valve. Especially the switching process of the high digital bits requires to be regulated to reduce the large overshoot. The above analysis contributes to the improvement of lubrication and sealing in water hydraulic control valves and applications of water hydraulics in the industry.