Based on analysis of the defects of home-made vacuum fish pump, an improved new machine with dual-vacuumizing method of discharging both air and water was designed and made, for the principle of creating vacuum by increasing vacuum space was widely applied at home and abroad. According to the program processing results and technical parameters of vacuum pump and water pump, fish pump was assembled and tests of pumping live fish were carried out in a pool. It was indicated that the curve of pressure variation in the tank fluctuated a little due to unstable discharging efficiency of the vacuum pump. However, the trends of both experimental and theoretical curves were almost same. Suction time with water pump ON was about 10s longer than that with pump OFF, which showed that the flow velocity in the suction pipe increased markedly. Therefore, the method using water pump to discharge water was effective to cooperate the vacuum pump to reduce the tank pressure, prolong the suction time and reduce the machine size. Shorter suction time and higher suction velocity could be obtained when initial tank pressure was set at 2mH_2O compared with 4mH_2O. 13 kg live fish (body length 150-180 mm) was pumped within 20 s by this pump and 2 t fish might be caught within 1 hr.