The invention discloses a simulation method of ultra wideband electromagnetic waves. The invention proposes a new PML method on the basis of the PML method under a stretch coordinate system and a difference scheme of a higher-order time domain finite difference method (FDTD (2, 2M)). A piecewise linearity convolutional perfectly matched layer (PCPML, Piecewise linearity CPML) under self-adapting absorption parameters absorbs a boundary condition. PML absorption factors are set to be adjustable parameters by the method so as to absorb different ultra wideband electromagnetic waves from high frequency to low frequency, and the parameters are obtained by a mixed method of an optimization method of a real coding genetic algorithm and a linear iteration method in a self-adapting manner so as to adapt to the absorption of ultra wideband electromagnetic waves. The absorption boundary condition adopted by the method can absorb and process high frequency waves and low frequency waves, and also can reduce the reflection error of a matched layer caused by grid dispersion and edge reflection and improve the absorption efficiency and the accuracy of simulation result.