A long sensing fiber was divided into 2 segments. An optical splitter was used to split a laser pulse into 2 channels which were connected with front and rear sensing fiber, respectively. Laser pulse was injected into the 10.7 km sensing fiber by a wavelength division multiplexer after transmitted through another 12.5 km dedicated fiber instead of the front 12 km sensing fiber. This method can effectively improve Raman signal intensity of the rear segment sensing fiber. 22.7 km sensing length was achieved with temperature measurement accuracy of ± 0.5 ℃ for both of the front and rear segment of the sensing fiber.