The invention discloses a true triaxial device for testing rock temperature and a heat conductivity coefficient under stress variation. The device comprises a triaxial cell and a temperature heating system; the temperature heating system closely encircles an external side wall of the triaxial cell; the temperature application values of the temperature heating system range from 10 DEG C to 150 DEG C; a thermometer is arranged above a side wall of the triaxial cell; an upper end and a lower end of the triaxial cell are respectively provided with an upper seat and a pedestal; a test space is enclosed by the triaxial cell, the upper seat and the pedestal; an upper end of a side wall of the test space is provided with an exhaust passage and a temperature sensor passage which are communicated with the exterior from inside to outside; and a lower end of the test space is provided with an oil pipeline and a wire arranging passage. The true triaxial device disclosed by the invention has the advantages that the structure is simple, the use is convenient and the accuracy is high. The invention further discloses a method of the true triaxial device for testing the rock temperature and the heat conductivity coefficient under the stress variation.