A high power pulse generator with peak power over tens of GW and repetitive rate of 5 Hz, named HEART-50, is studied theoretically, numerically, and experimentally. The generator is composed of charging source, primary compress switch, pulse forming line, main switch, impedance transmission line, and dummy load. Design considerations of the generator are discussed. Then key parameters which influence performance of the mixed-liquid-dielectrics based pulse forming line is numerically investigated. PSpice software is used to study the whole circuit of the generator. The HEART-50 has been built and experimentally studied in our laboratory. Quasi-square pulses with peak voltage over 520 kV, pulse duration approximately 90 ns, rise-time of 25 ns, and repetitive rate of 5 Hz, are achieved on the dummy load with good uniformity.