In order to make use of the distributed optical fiber strain sensing technology to measure the strain of the three core fiber composite submarine cable, the finite element method is used for modeling, solving and analyzing. The conductor screen, insulation screen, semiconductor resist layer and filling layer are merged to insulation layer. The model ignores the brass band, armored cushion, coating. The model is used to analyze the dynamics of the model by using the SOLID164 element. The uniform load is applied to the tensile simulation test . The strain of the copper conductor, XLPE, lead alloy, steel armor and optical unit is fitted by using the least square method. Their functions are obtained. The results of the model can meet the characteristics of elastic and plastic materials. It provides reference for mechanical properties research and operating condition judging of submarine power cable.