Based on the conservation of energy and the working characteristics of gears, the calculation formulas for the instantaneous flow and non-uniform flow coefficient in helical gear pumps with different gears are obtained. By calculating and analyzing the instantaneous flow and flow fluctuation characteristics of gear pumps with different tooth numbers and helix angles (spur gear pump with helix angle 0°), it can be seen that: If the driving gear has the same number of teeth, modulus, pressure angle, the non-uniformity flow coefficient of spur gear pump is relatively small; for helical gear pump with different number of teeth, the non-uniformity flow coefficient increases with the increase of helix angle and decreases with the increase of the number of gear teeth. And when the number of driving gear teeth remains unchanged, the flow non-uniformity coefficient increases sharply with the reduction of the number of driven gear teeth and the increase of helix angle, but it is independent of the gear modulus.