Abstract: This paper describes a nanosecond pulse generator using a spark gap switch and a short water line mediate storage (WLMS). Various voltage-gain (ratio of output voltage to DC charge voltage) of 1.2～1.6 times has been obtained by varying the value of the WLMS's solution resistance. The influence of the electrical parameters on voltage-gain coefficient K is discussed. A series of experimental investigations have been done at a coaxial test device and the voltage gain of 1.6 was obtained. Experiments show that three output trigger pulses of 50 kV have been obtained at 2.7 J storage energy. The jitter τ_j is less than 3 ns with a rise time τ_R less than 30ns. Based on these experiments, a new nanosecond pulse generator as an accurate trigger generator has been designed and construted. The repetition rate is from 0.5 Hz, 1 Hz up to 20 Hz and accumulative total charge-discharge times are 10⁷, 5×10⁴ and 10⁸, respectively.