The invention discloses a test power supply for high-voltage three-phase combined transformer verification. The three-phase inlet wire ends of three-phase AC power are connected with a main voltage regulator. The output end of each phase of the main voltage regulator is connected with an outlet wire end via an independent fine voltage-regulating unit. The main voltage regulator is a three-phase self-coupling voltage regulator. The fine voltage-regulating unit comprises an isolation transformer connected with the output end of the main voltage regulator and the outlet wire end of the test power supply through a secondary winding, and an auxiliary voltage regulator connected with the primary winding of the isolation transformer and the corresponding inlet wire end of the three-phase AC power. The auxiliary voltage regulator is a single-phase self-coupling voltage regulator. The test power supply for high-voltage three-phase combined transformer verification is wide in voltage regulation range, low in regulation fineness, and stable and reliable, and guarantees adjustable 1%IN and 5%IN measuring points and fine adjustable 20%IN, 100%IN, and 120%IN measuring points, and is very suitable for three-phase high-voltage combined transformer verification.