High temperature superconducting (HTS) power cable requires forced sub-cooled LN2 flow cooling. Liquid nitrogen is circulated by a pump and cooled back by cooling system. Typical operating temperature range is expected to be between 65 K and 77 K. The HTS power cable needs sufficient cooling to overcome its low temperature heat load. For successful cooling, the hydraulic characteristics of the HTS power cable must be well investigated to design the cables. Especially, the pressure drop in the cable is an important design parameter, because the pressure drop decides the length of the cable, size of the coolant circulation pump and circulation pressure, etc. This paper describes measurement and investigation of the pressure drop of the cooling system. In order to reduce the total pressure drop of the cooling system, the flow rate of liquid nitrogen must be controlled by rotational speed of the circulation pump.