The invention relates to the technical field of power transformer substation non-electricity protection, particularly to a transformer reactor temperature protecting device in-site detecting method. The transformer reactor temperature protecting device in-site detecting method comprises the following steps of 1) in-site environmental temperature testing, 2) thermostat temperature increasing, 3) indicating temperature reading and recording, 4) contact reading and 5) added temperature increase different comparing. Compared with the prior art, the transformer reactor temperature protecting device in-site detecting method has the advantages of being high in measuring precision and convenient to install, avoiding influence of high-altitude and cold environments on in-site detecting results of transformer reactor thermometers, and facilitating smooth operations of in-site detection of the transformer reactor thermometers in the high-altitude and cold environments.