A compact nanosecond pulse generator was developed, aiming at producing high-energy flash x rays with a long lifetime. The generator was designed on the basis of a 0.67-ns pulse forming line (PFL), which is charged to ∼700 kV by an air core Tesla transformer and switched by a fast spark gap. The Tesla transformer consists of a single turn primary coil surrounding a 44-turn secondary coil using no magnetic cores. 2D magnetostatic and electrostatic simulations were carried out, and the inductance and stray capacitance of the transformer were calculated. The transformer was powered by a 40-nF capacitor bank via a hydrogen thyratron. An effective coupling co-efficiency keff of 0.55 was achieved. The PFL voltage reached its second peak of 680 kV in 395 ns when the capacitor bank was switched at 25 kV. A nanosecond pulse with a peak voltage of 510 kV, a peak power of 2.6 GW, and a pulse width of 2.1 ns was generated on a 100-Ω ceramic resistor, which is going to be replaced by a vacuum x-ray tube. Since the pulse energy is small, the x-ray tube is expected to have a long lifetime. The generator is 285 mm in diameter, 800 mm in length, and 35 kg in weight, providing a compact means for high-energy x-ray radiographies both in scientific research and industrial applications.