Interventional needle shape monitoring method can provide doctors with important information during surgery and is a necessary means to ensure the safety of surgery. In order to improve interventional needle shape measurement accuracy, a fiber grating sensor (FBG) array was presented, which introduced a strain sensitivity matrix to measure the shape of the probe. Firstly, based on the theory of FBG, the relationship between the wavelength shift of the fiber grating implanted in the probe and its strain was analyzed, and the strain sensitivity matrix was introduced, the relationship between the FBG center wavelength shift and its bending curvature was studied. Then the geometric parameter relations and coordinate transformation equations of the needle's local elements were deduced, and the needle shape reconstruction model based on fiber grating was established. Finally, in order to verify the influence of introducing the strain sensitivity matrix on the shape measurement accuracy, the shape measurement experiment of the intervention needle implanted with the FBGs array under different bending states was carried out, and the error of the shape measurement before and after the strain sensitivity matrix was compared and analyzed. The experimental results show that the introduction of the FBG’s strain sensitivity matrix can effectively improve the measurement accuracy of the needle. Under different bending conditions, the average error of the end of the interventional surgical needle is reduced by 1.385 mm, and the maximum error is reduced by 3.317 mm. The shape measurement method based on FBGs array proposed in this paper has broad application prospects in the direction of shape measurement of flexible medical instruments in interventional surgery.