An open microfocus X-ray source and a control method thereof are provided. The open microfocus X-ray source includes: an open X-ray tube, a high voltage power supply (HVPS) system, a vacuum system and a control system. The open X-ray tube includes a cathode system, a deflection system and a focusing system. The HVPS system is configured to provide an emission current I0, an accelerating high voltage U0 and a grid voltage UG for an electron beam. The vacuum system is configured to perform vacuumization. The control system is configured to control, according to a spot size of an electron beam for bombarding an anode target, the HVPS system to adjust the emission current I0, the accelerating high voltage U0, a deflection coil current IXY of the deflection system, and a focusing coil current IF of the focusing system, such that the spot size meets a preset requirement.