To better evaluate the thermal safety risk of continuous flow reactions， a study was conducted using a tubular reactor as an example. By constructing a reaction system model based on heat balance and material balance， the actual heat transfer and thermal safety risk of continuous flow reaction systems were investigated. To address the adiabatic temperature rise reaction phenomenon at the inlet end of a channel reactor， a method based on the critical reaction half-life was proposed as a criterion for thermal safety assessment. Two major reaction conditions with high thermal safety risk were identified： when the total heat release of the target reaction is greater than 800 J·g^-1， and the reaction half-life of the reaction at the reaction temperature is less than the critical reaction half-life； when the total heat release of the decomposition reaction is greater than 800 J·g^-1， and the reaction half-life of the target reaction at the reaction temperature is less than the critical reaction half-life， while the reaction half-life of the decomposition reaction at 100% MTSR（maximum temperature that the process reaction can reach） is also less than the critical reaction half-life.Furthermore，the accuracy and practicality were verified through the nitration reaction of chlorobenzene，and the results show that an explosively decomposition reaction could occur in the channel reactor under these conditions，thus confirming the high-risk thermal safety conditions of continuous flow reactions determined by this evaluation method.