To acquire the characteristic parameters of plasma generated by hypervelocity impact, experimental system and a new Triple Langmuir probe diagnostic system are established in the paper. Triple Langmuir probe diagnostic technology does not require a voltage or frequency sweep compared to other Langmuir probe methods. The system allows the direct display of electron temperature and semidirect display of electron density by appropriate display system, this method eliminates the time consuming in data analysis required in curve-fitting current-voltage characteristics. As an example of application to timedependent plasmas measurement, the electron temperature and electron density of plasmas were measured in hypervelocity impact experiments. Experimental results show that the Triple Langmuir probe diagnostic technology can be well used to measure electron temperature and electron density of time-evolution plasma.