The performance of ML detection for the given channel is analyzed in spatially multiplexed MIMO system. In order to obtain the vector symbol error rate, we define error vectors which represent the geometrical relation between lattice points. The properties of error vectors are analyzed to show that all lattice points in an infinite lattice almost surely have four nearest neighbors after random channel transformation. Using this information and the minimum distance obtained by the modified sphere decoding algorithm, we formulate the analytical performance of vector symbol error rate(VSER) over the given channel. To verify the results, we simulate ML performance over the various random channels which are classified into three categories: unitary channel, dense channel, and sparse channel. From the simulation results, it is verified that the derived analytical result gives a good approximation for the performance of ML detector over all random MIMO channels.