With the requirements of high voltage field tests and insulation field tests, there is an increasing demand for the impulse voltage generators with high output capability and flexible characteristic. Therefore, this paper designs a 3000 kV/300 kJ vehicle-mounted impulse voltage generator, which adopts the integrated design for the main structure. The mechanical and electrical characteristics of this impulse voltage generator are analysed. The mechanical bearing margin and electric field peak position are calculated to validate the design of the key parts. Ten types of tests are carried out to demonstrate the verification. Results show that, the deflection at the end of the supporting tube is 75 mm. The bending stress is 8.3 MPa, of which the safety margin is 7.2 times. The output of the hydraulic cylinder on both sides is 38.6 WN, of which the safety margin is 1.3 times. The surface field strength peak is 20.4 kV/cm and locates at the metal flange connection of the pulse capacitor and resistor, which will not result in the partial discharge phenomenon. The impulse voltage generator can be transported horizontally and operated vertically. The material and structure design of the equipment can meet both the mechanical and electrical requirements.