Because of short circuit, overload, voltage and current instability, the transformer bank of coal-fired power plant often fails. In order to solve the problem of transformer fault, the relay protection measures of 110kV line, 220kV line, bus and main transformer were designed. The reliability curves of the four protections were analyzed by simulation. The simulation results showed that relay protection could further strengthen the power grid security and improve the stability of the coal-fired power plant.