Based on the temperature tunable principle of π phase-shifted fiber Bragg gratings, a thermo-electric cooler and a refrigeration wafer are used to control the temperature of a π phase-shifted fiber Bragg grating, and then change its central wavelength. Its central wavelength has a bathochromic shift with temperature rising. As the temperature rises from 0 ℃ to 95 ℃, the central wavelength changes from 1548.921 nm to 1550.664 nm with a total change of 1.743 nm. The sensitivity is approximately 18.35 pm/℃. In order to verify the temperature tuning properties of π phase-shifted fiber Bragg gratings, we design a C-band ring-cavity fiber laser by using high reflectivity fiber Bragg grating(FBG) with matched reflectance spectrum. We use narrow-band filtering characteristics of π phase-shifted FBG to realize narrow linewidth fiber laser output,and control the temperature to realize continuous tuning of output laser wavelength.