This paper proposes a dynamic congestion control algorithm for a reliable message transmission in V2V communication environment based on IEEE 802.11p WAVE technology. Each vehicle periodically exchanges its status information like a position, speed and break control with other vehicles within a communication range. Without any control, each vehicle always uses the maximum transmitting power and data rate. From our experiments, at heavy traffic flow, the higher transmitting power and the higher data rate makes the wireless channel contentions and packet collisions more serious. In this paper, we propose the mean-based dynamic data rate control algorithm and the phase control using epoch to mitigate the congestion. The performance evaluations in Qualnet confirm that the proposed algorithm achieves better communication performance than the existing solutions and is more robust to the hidden terminal problems.