Langmuir Probe (LP) has been extensively used on satellites and sounding rockets for in situ measurements of the bulk parameters of the space plasma, i.e., electron density and electron temperature. LP sensor is usually a metallic electrode immersed in plasma for electrons and ions collection. Though the structure of the sensor is simple, there are many complex complications having to be taken into account for the design and implementation of LP investigations. There are three main factors for the sensor design, i.e., the shape, the dimension and the surface. The shape of LP sensor is mainly determined by the LP theory and end effects; the dimension is mainly determined by the signal intensity vs. capacity of the electronics, the LP theory vs. plasma environments, and the satellites or rockets conducting surface areas vs. sensor effective areas; the sensor surface should exhibit inherently uniform surface potential. All the variety complex complications above have been analyzed carefully and a prototype Langmuir probe has been designed. A simulation of the proto Langmuir probe has been done by the SPIS software, which shows the feasibility of the design.