Abstract: Digital reactor protection system (RPS) is gradually replacing analog counterparts and being applied in newly-built and upgraded nuclear power plant (NPP), and the analysis of digital RPS reliability is one of the hot topics in the research field of NPP I&C. Based on RPS of high temperature gas-cooled reactor pebble bed module (HTR-PM), the research of this paper focused on development and analysis of digital RPS fault tree model, which was outlined as following: The top event for a fault tree was chosen; the method to build a fault tree model based on failure modes and effects analysis (FMEA) was studied, specially focusing on the sub-tree of redundant channel “2-out-of-4” logic and the fault tree under one channel bypass; the qualitative analysis of fault tree, such as RPS weakness according to minimal cut sets was summarized. The research is important to analyze digital RPS reliability and to improve its design.