As the core element of the hydraulic system, digital valve will lead to serious consequences if it fails. In order to improve the reliability of digital valve, the reliability of incremental digital valve was studied. The reliability block diagram of the digital valve was established based on the incremental digital valve mechanical structure and working principle, and the fault mode and fault mechanism were obtained through analyzing. The fault tree model of digital valve was established and analyzed. The criticality analysis of the influence of fault on the mechanism was carried out and the criticality matrix was obtained.The result shows that there are three kinds of common faults in the process of digital valve operation,such that the valve core does not move, the operation of the valve core is stuck, and the operation of the valve core is inaccurate. The valve core suddenly stuck in the process of running is the most serious fault mode in the criticality of digital valve. The research results can provide reference for structural design optimization and reliability analysis of incremental digital valve.