The principle of nano-indentation and the test methods to measure modulus of PBX are described. A 4×4 array of indention test with 10 μm separation was performed on the surface of a cylinder PBX sample with chief constituent of HMX crystals. The results show that that values of modulus decrease with the increasing of indent depth but,when the depth reach deeper than 750 nm,the measured values keep stable and the average value of 6.0 GPa is close to that of traditional method.