In this paper,the relationship between the output interference light intensity and the modular phase difference in panda fiber is investigated,and the modular interference patters are given.The propagation characteristics of several lower order modes in panda fiber are calculated with finite element analysis method.And the modular interference beat length of LP01and LP11is presented theoretically.An experiment is conducted to demonstrate that two-lobe interference output patterns oscillate with each other when the strain is applied on the fiber.And the simulation result of the modular interference beat length is validated also.The results in this paper provide theory foundation and experimental verification for building novel fiber-optic sensors based on the modular interference technology with panda fiber.