To determine the influence of the structural parameters of the cylindrical gear flowmeter and the physical characteristics of the fluid medium on its performance, and to determine the optimal assembly clearance, a simulation method based on the six-degree-offreedom motion model is proposed. Based on this method, the effects of different assembly clearances and different fluid viscosities on the performance of the DN16 cylindrical gear flowmeter are studied. The results show that the linearity error gradually decreases with the decrease of the assembly clearance. When the tip clearance is 140 μm and the gear end clearance is 100 μm, the linearity error reaches the optimal value of 0. 13%. The linearity error decreases with the increase of fluid viscosity. When the viscosity is 42. 7 mm 2 / s, the linearity error is only 0. 03%.