A novel reflex fiber optic pressure sensor used in the offshore oil exploration was proposed. Based on the original network compensation technique, the long term stability and the measurement accuracy of the intensity modulated fiber optic sensors were tremendously improved. The error compensation principle of the sensor was theoretically described. Preliminary experimental results indicated the feasibility and practicability, and the estimated pressure measurement accuracy will reach 0.1 MPa. The measurement stability can reach 0.15% when it was applied on the underground crude oil exploration.