The invention provides a temperature sensor and a temperature sensing system based on an active phase shifted grating, which belong to the technical field of optical fiber sensing. The temperature sensor comprises a pump laser, a wavelength division multiplexer, an optical detector and an active phase shift fiber grating with pi phase shift, wherein pump light emitted by the pump laser enters the active phase shift fiber grating through the wavelength division multiplexer; laser outputted after the active phase shift fiber grating absorbs the pump light enters the optical detector; the optical detector is used for measuring the output power of the active phase shift fiber grating to analyze the power to obtain the working temperature of the active phase shift fiber grating. Compared with a fiber grating sensor by using wavelength demodulation, the temperature sensor provided by the invention obtains the working temperature of the active phase shift fiber grating through analyzing the output power of the active phase shift fiber grating measured by the optical detector for realizing temperature sensing, the cost is low, integration is easy, carrying is facilitated, and the problem of reduced temperature measurement accuracy caused by strain-temperature crosstalk can be effectively avoided.