This paper is about a knee joint moment estimation algorithm which simplifies the calculation procedure by using only two surface EMGs. Parameters of two knee joint muscles calculated with an optimization process are applied to estimate the knee joint moment. The optimization process is based on the isometric knee motion data obtained from a dynamometer (CONTREX-MJ system) and MATLAB optimization toolbox. The developed knee joint estimating algorithm is evaluated by comparing the isokinetic knee motion experimental data with the estimated. In order to apply the proposed algorithm to the rehabilitation devices in a real-time environment, a knee joint moment estimator relying on look-up tables instead of the complex analytic muscle equations is developed.