The invention relates to the technical field of power transformers, and discloses a measuring method of an oil/gas sleeve outgoing line type transformer. The transformer comprises a main transformer primary side oil/gas sleeve and a main transformer secondary side oil/gas sleeve, which are connected to SF6 gas chambers, and the transformer is connected to GIS (Geographic Information System) equipment. The method comprises the following steps: S1, a main transformer primary side switch and a main transformer secondary side switch are opened when the main transformer primary side oil/gas sleeve, the main transformer secondary side oil/gas sleeve, the SF6 gas chambers and the GIS equipment are in a sealing state; S2, the short circuit of outgoing lines of the two sleeves and a neutral point of the transformer is realized by using an experiment wire; S3, a high voltage is applied to the neutral point of the transformer, the insulating resistance of a high-voltage winding and a medium-voltage winding to a low-voltage winding and the ground are respectively measured, and the insulating resistance of the low-voltage winding to the high-voltage winding and the medium-voltage winding are respectively measured. The method provided by the invention has feasibility, and is short in consumed time and low in cost.