We investigate the evolution of the decorrelation bandwidth of intercore crosstalk (IC-XT) based on the modified mode-coupled equations (MCEs) in homogeneous weakly coupled multicore fibers (WC-MCFs). The modified MCEs are numerically solved by combining the fourth order Runge-Kutta method with the compound Simpson integral method. It can be theoretically and numerically observed that the decorrelation bandwidth of IC-XT decreases with transmission distance by fractional linear function. The evolution rule of IC-XT's decorrelation bandwidth is further confirmed by experiments, which can be used as an evaluation criterion for the channel model. Finally, we propose a new channel model with the coupling matrix of IC-XT generated directly from the phase transfer function (PTF), which is in good agreement with the above evaluation criterion. We believe the proposed channel model can provide a good simulation platform for homogeneous WC-MCF based communication systems.