Agile high repetition rate discharge technology has important applications in improving plasma uniformity. SiC photoconductive semiconductor switch (PCSS) has the advantages of high breakdown field strength, high saturated carrier rate, high radiation resistance, high thermal conductivity and high temperature stability. It is an important solid-state electronic device to produce high repetition rate, high power and short width pulse. Operation characteristics of the MHz repetition frequency sub-nanosecond pulse generator based on vanadium-compensated semi-insulating (VCSI) 4H-SiC PCSS under high electric field are presented in this paper. 1 MHz, 1030 nm laser cluster driver with tunable optical pulse width is used for VCSI 4H-SiC PCSS response test. The 0.8 mm thick 4H-SiC PCSS can work with electric fields up to 200 kV/cm and the electrical power capacity up to 176 kW without failure for long time. The minimum photocurrent pulse width is about 365 ps and the jitter is less than 100 ps.