Abstract: The liquid metal loop is an essential experimental facility for carrying out key technological and experimental verifications of liquid metal spallation target. Gallium has lower melting point and very high boiling point, and is non-toxicity, so it could be used as a simulation medium in experiments of liquid metal loop. The design idea, structural component, basic function and operation process of a small-scale liquid metal gallium loop were described. The liquid gallium is driven by a variable frequency centrifugal pump to generate forced convection, simultaneously, the flow, pressure, differential pressure in the loop, and the position and shape of the free surface in the windowless target were measured. Finally, the changes of the pressure, differential pressure, and free surface position with the flow were analyzed. The results show that the free surface position depends on pressure and flow velocity.