Abstract: The rocket-borne Langmuir probe is developed and completed the flight test in Meridian Project.The flight test is the first application of Langmuir probe insitu measurement technology in China.The rocket-borne Langmuir probe sensor is a spherical sensor with the upper hemisphere for the collection electrode and the lower hemisphere for the protection electrode.The linear range adjustable micro-current measurement technology is designed to achieve a wide range of _ρA~_μA precision measurement.Two work modes including a scan voltage and a fixed voltage are designed to detect electron density,electron temperature and ion density parameters. The Meridian Project sounding rocket flight test is successfully completed in Hainan China on May 7,2011.The space area(longitude 109°,latitude 19.5°)plasma insitu data is obtained for the first time.