Based on conformal construction of physical model in a three-dimensional Cartesian grid, integral-based confor-mal convolutional perfectly matched layer (CPML) is given for solving the truncation problem of the open port when the enlarged cell technique conformal finite-difference time-domain (ECT-CFDTD) method is used to simulate the wave propagation inside a perfect electric conductor (PEC) waveguide, and the algorithm has the same numerical stability as the ECT-CFDTD method. For the long-time propagation problems of evanescent wave in a waveguide, several numerical simulations are performed to analyze the reflection error by sweeping the constitutive parameters of the integral-based con-formal CPML. Numerical results show that the integral-based conformal CPML can be used for efficiently truncating the open port of the waveguide.