Abstract: This paper presents a compact high-voltage nanosecond pulse generator, which combines high-coupling Tesla transformer with spiral forming line (FL). The spiral FL charged from the build-in Tesla transformer includes an outer shield cylinder, a spiral middle cylinder, and an inner conductor cylinder. At both sides of the FL, inner and outer cylinders are all short-circuit connected. One end of the spiral middle cylinder is open-circuit connected, the other end passes through short-circuit interface of inner and outer cylinders, and is connected to one electrode of the main switch. Such structure is simple and compact, which can generate high-quality pulse waveform with fast front and flat top. One design example of FL with Midel 7131 synthetic ester dielectric is given in the end of this paper, and the calculative and simulative results indicate that a pulse with 10 GW peak power and 100 ns width can be generated by the 2 m long FL with 0.88 m interior diameter of outer cylinder.