Abstract: One compact long pulse generator was presented, whose spiral pulse forming line consisted of an inner conductor and an outer shield composed of magnetic material. The spiral pulse forming line was charged by a built-in high coupling Tesla transformer, whose primary coil was adjacent to the outer shield and the secondary coil was located between the central spiral conductor and the outer shield. Theoretic calculation to characteristic parameters and numerical simulation of wave transmission on spiral forming line were given. The principle verifying experiment to generate a long pulse on a spiral line was proceeded preliminarily. The experimental results show that such structure design is feasible.