The disc-seal single screw pump (DSSP) used in the field of high viscosity oily sludge transport has a huge advantage. However, there is no research on the pressurization characteristics of the DSSP at present, which makes its application limited. In view of this, the pressurization process mathematical model of the DSSP was established based on the geometric model of the pump. By using this model, the pressurization characteristics of DSSP and the influence of working parameters on the pressurization process were studied combined with the principle of back-flow pressurization. Analysis results show that the instantaneous pressurization process could be realized mainly depending on the reflux pressurization from the outlet chamber to the pressurization chamber when the screw rotor rotating angle is located at −5° to +5°. The pressure in the pressurization chamber will increase with the increase of working parameters which include inlet pressure, outlet pressure, screw rotation velocity and dynamic viscosity of fluid medium in the area of flow-back pressurization. The screw rotation velocity and the viscosity of the conveying medium have significant effects on the peak pressure in the pressurization chamber, and the peak pressure in the pressurization chamber is proportional to the screw rotation velocity and the dynamic viscosity coefficient of the conveying medium. The proportional coefficient between the peak pressure and the screw rotation velocity is 6.29 × 104. The proportional coefficient between the peak pressure and the dynamic viscosity of the conveying medium is 6.28 × 106.