Abstract: Most of existing multicast congestion control mechanisms transmit multimedia services by simulating TCP windows mechanism.Although these mechanisms are friendly to TCP flows，the sending rate fluctuates sharply，which can not satisfy the demands that multimedia flow needs smooth transmitting rate and stable bandwidth.Based on fuzzy control theory，a multicast rate adjusting algorithm（FC-MRAA） is proposed for smoothness and TCP-friendliness.In the new algorithm，two fuzzy controllers are designed，one of which calculates the control parameter based on the feedback information from multicast receivers to keep TCP-friendly，and the other one computes the control gain to adjust sending rate further for smoothness based on the possession of router buffer.Simulation results show that the new algorithm has well smoothness and TCP-friendliness.