Abstract: In order to diagnose electromagnetic radiation generated by hypervelocity impact, the experimental and microwave diagnostic system for the electromagnetic radiation was established. Experimental diagnostics of electromagnetic radiation generated by impacting LY12 aluminum target were finished by using the microwave diagnostic system under loading velocities of 4.60 and 4.66 km/s separately. The relationship between electromagnetic radiation and target thickness was analyzed in the experiments. Experimental results show that, the microwave radiation intensity is large, when target thickness is small; the power of microwave radiation was proportional to the microcrack number generated by hypervelocity impact. Meanwhile, the physical mechanism of electromagnetic radiation generated by hypervelocity impact can be explained as thermal excitation produced electron and existence of crack created by impact.