The seepage field monitoring of sandy soil is a necessary and basic work for disaster prevention and mitigation in geotechnical engineering. A distributed temperature system with the carbon coated heating optical fiber (C-DTS) is proposed on the basis of summarizing the advantages and disadvantages of the existing monitoring methods. The monitoring principle of the method is presented and the concept of the eigenvalue of temperature （ ）is introduced based on the thermal diffusion theory and Ohm’s Law. After that, a seepage field simulation device for sandy soil and monitoring program are designed as well. An indoor test of the seepage monitoring is run, the linear relationship of the eigenvalue of temperature ( ) and the seepage velocity (V) is defined at different seepage velocities in sandy soil. The temperature descends as the seepage velocity increases, and their relationship complies with the formula derivation. The experiment results show that C-DTS can effectively improve the sensitivity of DTS monitoring and realize fully-distributed monitoring of seepage velocity in geotechnical engineering. Finally, some related research work for further applying to geotechnical engineering practice has been analyzed.