Abstract: A sweep Langmuir probe diagnostic system was designed to investigate the electron temperature evolution of plasma produced by hypervelocity impact of LY12 aluminum projectiles into LY12 aluminum targets. In the experiment, LY12 aluminum spherical projectiles were loaded by a two-stage light-gas gun, the incident angle of LY12 aluminum projectiles was 30 and the impact velocities were different. The relation between the electron temperature of plasma and the impact velocity for the whole physical process was obtained by treating the effective data, which at the given probe positions were measured by the designed diagnostic systems.