The invention relates to a method for solving copper conductor temperature by optical fiber temperature for photoelectric composite submarine cables. The method mainly comprises the following steps: (1) listing the thermal load operating current range, ambient temperature range, environment convection heat exchange coefficient range during operation of the photoelectric composite submarine cable, and carrying out uniform discretization respectively; (2) using the optical fiber temperature Tf and parameters I, G and H as the input variable X, and the copper conductor temperature Tc as the output variable; (3) through a test, measuring and acquiring the output optical fiber temperature Tf and the copper conductor temperature Tc under different thermal load operating current I, ambient temperature G and environment convection heat exchange coefficient H of the photoelectric composite submarine cable, wherein X and Tc form mx*n*p input-output sample pairs; (4) selecting a Gaussian function based on a radial basis function of a multilayer feedforward neural network; (5) studying the m*n*p input-output sample pairs by the multilayer feedforward neural network, wherein the study algorithm is a nearest neighbor clustering algorithm, the values of wi, ci and sigmai are obtained after studying, i=1, 2, 3,...N; and (6) solving the copper conductor temperature Tc from I, G, H and Tf by using a formula.