Dissolution process of polystyrene in decahydronaphthalene solution was conducted and compared under different conditions. The effects of dissolution time and temperature on the dissolution ratio of polystyrene were performed with the assistance of ultrasonic and mechanical agitation, respectively. The dissolution ratio of polystyrene increased with the increment of dissolution time and dissolution temperature, polystyrene dissolved faster under ultrasonic-assisted process. The polystyrene dissolution kinetic model was developed and used to calculate the dissolution rate constant. The kinetic model showed good agreement with the experimental data, and the dissolution rate constant indicated that ultrasonic can obviously enhance the dissolution process of polystyrene in decahydronaphthalene solution.