Young′s modulus is a key characteristic of material, which can be got by strain and load of material. Because the flexible solid fuel is soft and incendive, traditional measurement method using strain slice is unsuitable. So a new method should be put forward. In this paper, optic fiber F-P strain sensor is stick on the surface of the flexible solid fuel to measure the strain of flexible solid fuel. And the weights supply load. Theory analysis is carried on. Experiments demonstrate that the measurement standard deviation is about 23.04 MPa and receivable, and the measurement method using optic fiber F-P strain sensor is agreeable.