Abstract Based on the investigation of Multiple-Input Multiple-Output (MIMO) technology and Ultra-Wide Band (UWB) wireless communication systems, a novel MIMO UWB system is proposed, which based on adaptive modulation technique in time varying channel. By using Singular Value Decomposition (SVD) theory and rate quantization methods, the joint time slot average power control algorithm to allocate power and rate is proposed. Simulations indicate that system performance is highly improved by using the power control algorithm.