An improved spiral generator is studied to solve the problem that the second peak value of output voltage waveform is larger than the first peak value and the peak current of input switch and its current rise rate are larger when the number of turns of the traditional spiral generator is large. Numerical simulation and experimental verification are carried out, and the simulation results are basically consistent with the experimental results. Through electromagnetic field analysis of the wave transmission process, it is shown that the additional winding of the improved structure will cause extra reflection, which changes the time when the voltage between the layers is superimposed in the same direction, thus reducing the subsequent oscillations of higher peaks. Finally, an improved spiral generator is tested and it can generate a high voltage pulse with the first peak voltage of 51 kV and the leading edge of 50 ns on a high voltage capacitor load of 15 pF. The volume of the whole generator is less than 0.5 L. The improved spiral generator will then be combined with the semiconductor switch to achieve an all-solid-state design of a high-voltage nanosecond pulse trigger generator in the future.