Abstract: In this paper, the development process of vacuum interrupter for 15 kV/6 300 A/80 kA generator is described from the viewpoint of tests and in combination with the problems in the process of large capacity interruption. First, based on the difficulty and parameters of the tests, it is concluded that the system source short-circuit break T100a is the most strict test method, and the main test parameters different from normal circuit breaker are analyzed. Then, the magnetic field amplitude and distribution of the vacuum interrupter before optimization are simulated and analyzed, and T100a with long arcing test is carried out on a test prototype. The test waveform and the contact condition after the breakdown of the arc extinguishing chamber are deeply studied and analyzed. It is preliminarily determined that the arcing energy concentration reduces the recovery speed of the back-arc medium in the contact gap and causes the break failure under the long arcing time. Based on the above analysis, the structure of vacuum interrupter is optimized from the aspects of contact diameter, magnetic field amplitude, strong magnetic field area distribution, main shield cover material and thickness, CuCr alloy contact material, and process selection. Finally, based on an improved vacuum interrupter, the test of T100a with long arcing is carried out again and passes successfully, which verifies that the short-circuit current margin factor of 1.29 times proposed in this paper is feasible. At the same time, it is also verified that, under the condition that the contact diameter is 160 mm, the area covered by the strong magnetic field greater than 4 mT/kA is 31.6%, the magnetic field amplitude reaches 5.5 mT/kA at the time of peak current, and the product can reliably break 80 kA short-circuit current. The research results provide an important basis for design of vacuum interrupter of large capacity generator.