The fully-leaky optical guided wave technique was employed to measure the sum of splay and bend of flexoelectric coefficients in the negative nematic liquid crystal MS-N01300-000.The curves of reflectivity versus the internal angle (the angle of incident light to liquid crystal) with different flexoelectric coefficients under the same value of voltage can be calculated by the elastic theory of liquid crystal and the multi-layer optical theory.The director profile of the mentioned liquid crystal parameter filled in hybrid aligned nematic liquid crystal cell for different external applied voltages can be reflected by the curves of reflectivity versus the internal angle using the fully-leaky optical guided wave technique experimentally.There is a small move for the curves of reflectivity versus internal angle when alternating current voltage or direct current voltage with the same value is applied to the hybrid aligned nematic liquid crystal cell,which is induced by the flexoelectricity of liquid crystal.The approximate value of the sum of splay and bend of flexoelectric coefficient of MS-N01300-000 is 2.5×10-11 C/m by comparing theoretical results with experimental data.