A high power fiber cladding optical filter with phase change material is designed and developed for the thermal managements of high power fiber laser in the space and other special environments. The phase change material of 18-alkanes is applied to absorbing cladding light heat. The Fluent module of Ansys is used to simulate the phase change process of phase change material and the temperature variation of the stripper at 200 W. 18-alkanes with the mass of 0.246 kg and the mass fraction of 99% is used as the phase change material. The experiment verifies that the stripper can work stably for 360 s at the room temperature of 25.6 ℃ and the light power of 206 W. The simulation results are basically coincident with the experiment.