The invention discloses a compact high-voltage controllable Marx generator which comprises a charge power supply, a charge resistor, a sphere-gap trigger switch, a withstand voltage capacitor set, (N-1) capacitors, (N-1) spark switches, 2N resistors and steep gaps, wherein the charge resistor, the sphere-gap trigger switch, the withstand voltage capacitor set, the capacitors, the spark switches and the resistors are all arranged in a sealed metal barrel; the sealed metal barrel is filled with mixed gas of liquid nitrogen and sulfur hexafluoride; the steep gaps are used for outputting steep leading edge high voltage pulses. The compact high-voltage controllable Marx generator is high in reliability, small in size, steep in pulse high voltage leading edge and low in construction cost.