Abstract: The eigen values of linear polarized mode (U,W) are calculated based on the eigen value equations of linear polarized mode of multimode fiber. The situation of power distribution of different modes is obtained when put the results into the power distributing function of fiber. With the use of fiber coupling equation, the coupling coefficient of every mode is calculated. The coupling efficiency and length of coupling fiber are calculated in different conditions. Depending on the analysis of numerical value, how to improve the efficiency of multimode fiber coupling is summarized. The result reflects that, for manufacturing the fiber coupler or combiner, it is necessary to consider the relation between fiber parameters and length of coupling fiber to achieve the optimal coupling.