The invention discloses a linear oil temperature loop tester. The linear oil temperature loop tester comprises three resistance output ends, a main resistor, a temperature gear switch group and two fine adjustment switch groups; two resistance output ends are connected by use of a short-circulating wire, and the main resistor, the temperature gear switch group and the two fine adjustment switch groups are connected in series between one resistance output end and the third resistance output end. The linear oil temperature loop tester is provided with three resistance output ends, wherein two resistance output ends connected by use of the short-circulating wire can be short-circulated by use of a loop resistor of a tested loop so that the error interference can be removed and the detection accuracy can be improved; a plurality of equivalent measurement resistance values in the range of 0-100 DEG C are provided according to a Pt100 resistance indexing gauge between the two resistance output ends connected in series with the main resistor and a knob switch so as to comparatively detect and determine whether the temperature change of the tested object is normal. The linear oil temperature loop tester is stable in performance, simple and convenient to operate and good in linearity. The linear oil temperature loop tester is used for greatly improving the oil temperature defect elimination efficiency of a transformer.