With the improvement of power density of internal combustion engine, the coolant jacket structure is becoming more and more important. The design and optimization of coolant jacket depend heavily on the construction and position of the upper-nozzles, so that the flowrate measurement in the upper-nozzles will benefit those design and optimization. However, during the flowrate measurement, the construction parameters and installation parameters of the measurement rig will affect the measurement error significantly. This paper explored the relationship between these parameters and the measurement error by means of CFD numerical simulation based on orthogonal design method. In order to control the measurement error in 3%, the flow in many upper-nozzle schemes were simulate, and then the range analysis of the simulation results were achieved and the levels of each factor were optimized. After the optimization, the suitable levels of each factor were determined, and the maximum measurement error of the optimum schemes was reduced to 2.95%. At the end, the paper achieved a measurement experiment to correct the numerical simulation, and the difference between simulation error and experimental error was only 2.07% according to the experimental results, which verified the reliability of the numerical simulation and accuracy of the measurement technology.