The electric field measurements in corona discharge provides a complementary results for the corona discharge study because the classical theory based on the current and voltage data is unsatisfactory. A new method of current density and field measurement with a linear biased probe, during the corona discharge, is developed in this paper. The work has elucidated the phenomenon of probe end-effects using a new profile of probe adapted to linear geometry. The probe functions were verified and the present theoretical model, which simulates the biased probe by the coplanar planes system, is thus verified. Other tests have been carried out with a wire-to-plane electrode system at various parameters. It has been shown that the measured field at the plane increases linearly with the corona voltage and it decreases as we move away from the centre of plane. The electric field at the plane decreases also as the distance between the wire and the plane increases.