The utility model provides a thermal relay, which comprises a three-phase bimetallic strip, a driving push rod, a differential push rod, a first pull rod arranged on the driving push rod, a link rod and a switching part. One end of the link rod is provided with a second pull rod, and the other end of the link rod is pivotally connected with the differential push rod. The first pull rod and the second pull rod are respectively used for pushing a tripping mechanism to drop out. The switching part is used for switching the driving push rod and the differential push rod between a phase-lack protection state and a non-phase-lack protection state. When the switching part keeps the middle part of the link rod to be disconnected with the driving push rod, the driving push rod and the differential push rod are set in the non-phase-lack protection state. The driving push rod drives the first pull rod to push the tripping mechanism to drop out. When the switching part keeps the middle part of the link rod to be connected with the driving push rod, the driving push rod and the differential push rod are set in the phase-lack protection state. Therefore, upon the occurrence of the phase-lack condition, the driving push rod pulls the middle part of the link rod to enable the link rod to rotate pivotally around the other end thereof. As a result, the second push rod pushes the tripping mechanism to drop out.