The properties of space charges formed in the hot compression molding process of low density polyethylene (LDPE) have been studied by measuring the open-circuit thermally stimulated discharge (TSD) current， in situ TSD charge and the isothermal charge decay. The results showed that the space charges with high stability at room temperature (RT) are trapped in two kinds of traps: shallow traps and deep traps with central depths of about 0.92eV and 1.31eV, respectively. Preliminary analysis indicates that the shallow traps and deep traps should be located in the surface layer and in the bulk of the sample, forming surface traps and bulk traps，respectively.