In order to solve the problem of cross sensitivity of temperature and strain that generally exits in fiber-optic sensor, the strain and temperature sensing characteristics of LP01 and LP02 mode interference based on the inter-modal interference principle of the few mode fiber are studied, and phase sensitivity theory of inter-modal interference sensing is analyzed in detail. A temperature-insensitive strain-sensing few mode fiber with core diameter of 15.1 μm, core refractive index of 1.4512 at 1550 nm and cladding refractive index of 1.444 is designed based on the numerical simulation results of the few mode fiber. The experimental system is built to research the strain and temperature sensing characteristics of few mode fiber. The results show that the theoretical calculation can predict the experimental result well. The phase sensitivity of the strain in the few mode fiber is 0.0196 rad/μm in the range of 0~600 μm, which is insensitive to the temperature in the range of 30~330 ℃. It can effectively improve the problem of cross-sensitive of temperature and strain.