The invention discloses a method and a device for judging whether a transformer requires an outage test or not. Three kinds of abnormal data of online oil chromatography, bushing dielectric loss and winding temperature of the transformer with a fault in history are selected; proper characteristic parameters are selected; the importance degrees of the abnormal data on the fault influence are analyzed; normalization processing is conducted on various online monitoring data generated for the transformer in one day to obtain normalized data; a weighted average value is calculated for the oil chromatography data; the importance degrees are multiplied by the normalized data and the weighted average value to serve as inputs for constructing an output Z; and the constructed output is compared witha determined threshold value T to judge whether the outage test is carried out or not. The method and the device disclosed by the invention have the advantages that a traditional mode that the outagetest is carried out according to a fixed period is changed, and whether the outage test is carried out or not is determined according to a judgment result, so that certain unnecessary outage tests are avoided, and certain non-timely outage tests are avoided.