Hydrogen production by water electrolysis is one of the promising ways for sustainable energy. The influences of magnetic field on the covering ratio and the upward velocity of the bubbles during water electrolysis in different working conditions are investigated by the use of a high-speed camera. Results show that the upward moving velocities of bubbles are increased while the covering ratios of bubbles are increased, under different inter-electrode distances and current density under the magnetic effect. The bubbles are more uniformly distributed on the electrode and the corresponding averaged diameters are decreased. At an inter-electrode distance of 2 mm and current density of 0.3 A/cm(2), the bubble flow rate is increased by 67.8% as the magnetic field is added, while it is about 42.0% at an inter-electrode distance of 5 mm and current density of 0.3 A/cm(2). Without extra energy consumption, the addition of magnetic field to increase the efficiency of hydrogen production by water electrolysis is proved.