The invention relates to a porous polymer material used for preparing a supercapacitor electrode and a preparation method thereof. Nucleophilic substitution reaction is carried out on bisphenol-like monomer containing a bis-phthalazinone structure and 4-halobenzonitrile in an aprotic polar solvent under the catalytic action of alkali metal halide, so that a series of novel dinitrile monomers containing the bis-phthalazinone structure are obtained; high temperature polymerization is carried out on the novel dinitrile monomers under the catalytic action of Lewis acid, so that a porous polymer material containing the bis-phthalazinone structure and a s-triazine structure is obtained; and the porous polymer material is assembled into a supercapacitor, and electrical properties of the supercapacitor are tested. The preparation method of the porous polymer material is simple and easy to control, and implementation of an engineering technology is facilitated; and the supercapacitor prepared from the porous polymer material has the characteristics of high specific capacitance (the specific capacitance is 378F/g when the current density is 0.1A/g) and excellent cycling stability (the specific capacitance is not attenuated after charging and discharging are carried out for 10000 times).