Rate control is an important technique in Constant Bit Rate(CBR) coding. AVC standards contains several inter and intra prediction modes. The current AVC software is difficult to adopt the existing rate control techniques, because the Rate Distortion Optimization (RDO) based on prerequisite quantization parameters determines the optimal prediction of each macroblock. This paper proposes an efficient rate control algorithm at macroblock level for AVC standard by considering adaptive quantization parameter. Experimental results show that the proposed rate control algorithm can accurately achieve the target bit rate. Although the PSNR of object quality of video sequences is degraded a little degraded, but the coding efficiency is similar to or better than of the fixed quantization parameter video coding.