Gap test was used to study the shock sensitivity G₅₀ of composite charge composed of Ф20 mm×20 mm JO-9159 and extrusion-cast explosive (ECX) with thickness of 3, 5, 10, 20 mm. The shock sensitivity of composite charge was simulated by LS-DYNA finite element method and compared with the experimental results. Results show that there is a good agreement between experimental and simulated results. The G₅₀ of composite charge is between that of JO-9159 and ECX, and it descends with first order exponential decay form of G₅₀=12.96+5.13e^-h/6.41 with the thickness of ECX increasing.