Crop wet biomass measuring with dielectric spectroscopy is a non-destructive method to quickly and accurately estimate plant biomass in situ. It optimizes the management of agronomists. An electrostatic free-space system was designed and tested to estimate crop wet biomass in situ. It acts as a parallel plate capacitor. The appropriate size of plate of the system is determined through Finite element analysis (FEA). Water is used to make the exclusion of interference at the earlier stage of the experiment, and Wheat is the experiment material. Results from the measuring system showed The Susceptance through the system was strongly correlated with wet biomass. The coefficient of determination (r2) is greater than 0.9.