An improved cavitation model was proposed to simulate the cavitation phenomenon in a water jet added with turbulent drag-reducing additives. The Cross model which expressed the shear-thinning properties of drag-reducer solution was also employed. The neglected viscous term and surface tension term in traditional cavitation models were reconsidered as viscosity, and surface tension force were important factors affecting bubbles' motion in drag-reducer solution. The numerical solutions of bubble radius in drag-reducer solutions of different concentrations were fitted, and the change rates were added to the original mass transfer mechanism equations. The results showed that the modified cavitation model described the cavitation characteristics in drag-reducer solutions more accurately and effectively reflected that the cavitation region's wake became longer with the increase concentration of the drag reducing agent. When the concentration increased, the distribution of cavitation cloud became more homogeneous, and the pressure curve and velocity curve both changed more smoothly.