The propagation and switching of short optical pulses in a three-core nonlinear fiber coupler have been investigated with a variation method within the framework of the Lagrangian density formulation.The analytical solutions were directly obtained from the coupled nonlinear Schr?dinger equations.It is shown that the soliton switching behavior predicted by the present analytical method agrees well with the results from numerical analysis.In addition,the coupling length and the switching threshold of solitons in a nonlinear coupler were obtained.