To study the effect of the number of blades and guide vanes to the reactor coolant pump radial force under variable flow transition conditions, applying computational fluid dynamics software CFX to the numerical simulation and test of the blades and guide vanes radial force variation, when changing the number of blades or guide vanes. Compared the numerical simulation results with the experimental results, the experimental data error within the control of the numerical simulation data. The results showed that: with the number of blades varying and the flow rate increasing, the radial force of the reactor coolant pump impeller increasing with the number of blades, and reaching the maximum in the number of 7, the periodicity of the impeller to withstand the radial force tends regularity, radial force balance tends to the optimum working condition. With the flow rate decreasing, the position of the impeller radial force offsets and rotates regularity in the spin cycle, and the variation gradient of the offset and rotation is different. The variation gradient of the impeller radial force offset and rotation is significantly greater than the variation gradient corresponding to the large flow increasing. Seen from the comprehensive comparison: when the number of blades is five and the guide vanes is 11,the radial force on the impeller is the minimum.