Abstract: A weak force of static electric field coming from weak electric field is used to make torsion balance device cause small angle of deflection, and then an optics plane mirror amplification is used to make small angle change into a horizontal displacement. Through the comparative method of this kind, the measurement of weak static electric field less than 1 V/mm is realized, the phenomenon is visual and the results are reliable.

Key words: weak electric field, Cavendish torsion balance, angle deflection, reflection of light