The invention relates to a urea crystallization risk prediction method of a Urea-SCR post-treatment system. According to the method, the level of the urea crystallization risk of the post-treatment system is judged according to CRF, if the CRF is larger than A2, it is judged that no urea crystallization risk exists, if the CRF is greater than or equal to A1 and less than or equal to the A2, it isjudged that the urea crystallization risk is low, and if the CRF is less than the A1, it is judged that the urea crystallization risk is high, wherein the CRF is any one of the ratio of the amount ofheat in the exhaust to the sum of the amount of heat required by evaporation of an aqueous urea solution and hydrolysis of urea, the ratio of the amount of heat in the exhaust to the amount of heat required by evaporation of water in the urea, the ratio of the amount of heat in the exhaust to the amount of heat required for hydrolyzing the urea into HCNO, the ratio of the amount of heat in the exhaust to the amount of heat required for hydrolyzing the urea into NH3, and the ratio of the amount of heat in the exhaust to the amount of heat required for hydrolyzing the HCNO into the NH3. According to the method, the real-time prediction of the urea crystallization risk during operation of the working condition is achieved.