Abstract: Unsteady flow caused by runaway/overload of mud pump can seriously damage the equipment, easily raising security risks in drilling operations. This study constructs a mathematical model for predicting surge pressure in pump suction line caused by accidents such as runaway/overload of mud pump in drilling operations. Model construction is based on considerations of drilling mud compressibility and drill string elasticity, combined with special structures of wellhead mud pump and its pipeline. The proposed model is solved using computer programming through an example study. Under standpipe pressure of 18 MPa, surge pressures caused by runaway and overload of dual mud pumps are up to 6.77 and 11.59 MPa, respectively. With increasing number of mud pumps, the inertia in high-speed operation of mud pumps is increased, thereby elevating surge pressure in the pipeline. With increasing length of the pipeline, the frictional resistance of fluctuating pressure is increased, while its conversion from kinetic to pressure energy is reduced. These changes ultimately result in a reduction in fluctuating pressure and a time lag in fluctuating pressure super imposition in the pipeline.