This paper presents an analytical model for ad hoe networks equipped with multiple-input multiple-output (MIMO) radios using spatial-multiplexing (SM). in particular, we consider the V-BLAST technology, nodes use this technology in PHY layer to communicate with each other. this model considers detection error spread effect of PHY layer, and combines with probability analysis of node action under a specific MAC protocol. based on this model we extend NS2, and contruct a general purpose simulation platform for wireless network design using MIMO. theory analysis and simulation show that this model can effectively support cross-layer protocol design of ad hoc networks.