In order to meet the measurement requirements of gas turbine tip clearance, the displacement optical sensor with two-circle reflective coaxial fiber probe is designed. Output functions of the fiber sensor without and with collimating lens are gained based on light intensity coupling principle analysis. The effect of lens on reflective optical fiber displacement sensor characteristics is analyzed. Then, effect of transmission efficiency and interference on measurement results is evaluated. The static measurement and smog interference experiment of the sensor with and without collimating lens are completed. The results show that the linear measuring range of the sensor designed is 2.6 mm, and the antipollution ability is proved. It provides a reference for the application of reflective optical fiber displacement sensor in gas turbine tip clearance environment.