Abstract: Aiming to the high-reliability and high-safety requirements of steam turbine protection system, anemergent trip system (ETS) based on the triple modular redundant (TMR) tolerant technology is presented in detailin this paper. The signal sampler, system bus, main controller, and output module are designed in TMR structure. Amethod of self-monitoring of intra-channel and cross-monitoring of inter-channel with synchronization strategy ispresented to realize fault processing and isolation. Through setting voting process in input data, output data, andH-pattern hardware structure, and adopting preset adaptable voting mechanism, the two failures-operation and threefailures-safety of the ETS system are realized effectively. Taking into account of maintenance, reliability and safetyreguirment of the system are analyzed based on the Markov model. Simulation results show that the system has ahigh reliability and high safety. Field commissioning and longtime electrified trials prove that the system satisfiesthe requirement of ETS safety protection system.