Pre-coding type can be grouped into two approaches, unitary or non-unitary for 3GPP Long Term Evolution(LTE). Output SINR of unitary Pre-coding for MU-MIMO is investigated in this paper. A more simple method of calculation for SINR is presented, which Leads to the computational complexity down to 18% compared with original method, while calculating MIMO Pre-coding system with 4 matrices (i.e. 8 vectors). In addition, we also analyzed the loss of SINR when using unitary or non-unitary Pre-coding. Corresponding simulations show that output SINR of non-unitary pre-coding system is inferior to the unitary pre-coding case and such losses can been described using statistical linear approximation.