There are no uniform national standards in the doublecone flowmeter. Research of the influence of the four geometric parameters, such as the front cone angle, the rear cone angle, the channel length, and the equivalent diameter ratio, on the performance index of the discharge coefficient and the pressure loss are helpful to its performance evaluation and calibration. Four groups of FLUENT fluid simulation experiments were designed by using the control variable experiment method, and the influence of each geometric parameter on the performance index was researched. The experimental results show that the influence of the front and rear angle has little effect on the outflow coefficient, and the relative pressure loss is the smallest when the cone angle is 45°. The channel length has the greatest influence on the outflow coefficient, but does not affect the linearity of the outflow coefficient, and also has influence on relative pressure lose. The larger the equivalent diameter ratio, the greater is the outflow coefficient, the smaller is the relative pressure loss, and with the linear relationship. Based on this, determine the flowmeter optimization parameters for the front and rear cone angle 45°, channel length to take D/2. Finally, a mathematical model of the equivalent diameter ratio and the discharge coefficient and the pressure loss is established under the optimized parameters of the double cone-flowmeter.