Distributed fiber optic sensor(DFOS) hasadvantage of leak detection in the buried thermal pipeline. However, limited by the spatial resolution, the distributed sensors have low accuracy to detect the local temperature variation caused by small leak, which makes the temperature measurement quite different from the practicaltemperature field. To solve this problem, one kind ofmethod is proposed to establish the correspondence between thesetwo temperature fields. Laboratory experiments and field tests are designed to simulate the actual leakage, where Raman optical time domain reflectometer(ROTDR) and thermistors are employed to measure the temperature. The extracted features based on the mapping relation between the actual temperature field and the DFOS measurements aredetermined using artificial neutral network(ANN). Experimental results show that the proposed ANN model is effective to establish the relation between the actual and measured temperatures. The measurement accuracy of ROTDR is improved from the aspects of data processing which provides valuablereference for small leak warning.