The invention discloses a lightning arrester on-line temperature measuring device based on a surface acoustic wave sensor. The lightning arrester on-line temperature measuring device comprises a control assembly and a sensor assembly arranged in a valve slice gap in a lightning arrester. The control assembly comprises a controller and an external receiving antenna connected correspondingly with the controller; the controller is communicated with a remote computer through a wireless communication module; and the sensor assembly comprises a surface acoustic wave temperature sensor and a conductive and heat-conductive package piece for installing the surface acoustic wave temperature sensor. The conductive and heat-conductive package piece is provided with a slot; the surface acoustic wave temperature sensor comprises an induction base and a signal transmitting antenna arranged on the induction base; and the induction base is inserted into the slot. The device, with the lightning arrester and the temperature measuring sensor being integrated, is simple in structure and convenient to install, realizes on-line measurement of temperature in the lightning arrester, and overcomes the defects that temperature measurement has an influence on lightning protection effect of the lightning arrester body, and the sensor is not easy to install in the prior art.