In this paper, a narrow linewidth single frequency distributed Bragg reflection (DBR) fiber laser was fabricated using Er:Yb codoped fiber. The laser was pumped by a semiconductor laser operated at 980nm and an output power of 2 3 mW with linewidth less than 5 MHz was obtained when pump power is 75 mW. Wavelength of the laser is 1557 524 nm. An active fiber sensor based on the DBR fiber laser was applied for temperature sensing and the experimental results show good linearity. This system has the merit of easier wavelength detection owning to its high signal to noise ratio and output power.