The spacecraft operate under complex space effects, with the interaction between charged particles and dielectric being the primary cause of charging phenomena and subsequent discharge events. This study analyzes the charge transport mechanisms in polymer dielectrics, aiming to elucidate the regulatory role of charge trap characteristics in charge accumulation and secondary electron emission (SEE). Thereby providing a theoretical foundation for suppressing surface discharge phenomena. Four typical polymer materials used in spacecraft—polyimide (PI), polyester (PET), polytetrafluoroethylene (PTFE), and polyethylene (PE)—are selected, and their trap parameters are measured using the photo-stimulated discharge. The obtained parameters are used as input data for subsequent simulation. A drift-diffusion simulation model is developed to quantitatively describe the self-consistent charge transport of electron–hole pairs, highlighting how charge traps influence the rate and extent of charge accumulation. A trap-modulated SEE model is proposed, elucidating the relationship between traps and secondary electron emission to electron avalanche. By using the measured trap parameters as inputs for the above simulation, the charge accumulation and SEE characteristics are computed and, subsequently, compared with experimental results of them, thereby revealing correlations between trap parameters and both charge accumulation and SEE characteristics. In particular, the surface charge accumulation rate, steady-state potential, secondary electron emission yield, and sample current follow the order PI < PET < PTFE < PE, which shows a negative correlation with charge trap density. While the flashover voltage follows the reverse order. This study provides theoretical principles for designing dielectric materials that suppress surface discharge in spacecraft applications.