A programmable wavelength widely tunable Er-doped fiber laser is demonstrated. The wavelength scanning tunable range can cover above 51 nm (from 1516.8 nm to 1568.3 nm) controlled by software and tunable step is up to 0.01 nm. Wavelength repetition scanning tuning can be controlled by programming. The laser is applied to the optical fiber grating to form a quasi-distributed temperature sensing system, which is applied in real-time temperature monitoring of 48 points in 16 channels. Because of the high output power, the detecting distance can be very long. When the output power is 20 dBm and the sensitive is －20 dBm, the detecting distance of the temperature sensor is more than 50 km. The temperature sensing system has important application in smart grid sensing system.