Effective operation risks evaluation of weaving areas of expressway can provide a basis for the optimization design for traffic organizations and the traffic control. Based on Tongji University 8 degree of freedom driving simulation platform, 16 simulation scenario of urban expressway weaving area were made based on the variation of weaving area length, traffic flow density and driving path. 20 samples’s operation conditions were simulated in these simulation scenario. The vehicle operation status characteristic was analyze, then the operation risk evaluation index was proposed. At last, the grading method of risk evaluation index was proposed based on the relationship analyze between risk index of operation safety(RIS) and scene variables. The research results show that the operating risk in the high-density traffic flow condition is 50% greater than that in the low-density traffic flow condition. RIS has a linear negative correlation with the length of the interlaced area. Increasing the length of the weaving area is beneficial to reduce the operational risk of the weaving area.