A subsection alternating current voltage withstanding test facility for a 750kV insulation tool and instrument comprises nine lifting supports, 14 sets of clamping plate electrodes, three sets of grounding devices and a cylinder electrode. The nine lifting supports are arranged on the ground with the transverse row* the longitudinal row of 3*3. The clamping plate electrodes are fixedly arranged at the tops of the lifting supports, the lifting supports comprise bases and height-adjustable insulation supporting rods arranged on the bases, and supporting plates are arranged at the upper ends of the height-adjustable insulation supporting rods. The three lifting supports of the front transverse row are respectively provided with a set of grounding device, one ends of the grounding devices are connected with the supporting plates, and the other ends of the grounding devices are connected with chassis, where the supporting plates are located, of the lifting supports. Two high-voltage voltage-dividing leads are led out of the two ends of the cylinder electrode respectively, and the length of each clamping plate electrode of the front transverse row and the rear transverse row is 2.4 m. Under the condition of a 500kV test transformer, the test length of 4.7 m under full voltages is met, meanwhile, the tested insulation tool and instrument is divided into even sections of 1.2 m, and a subsection test is carried out.