Abstract: This paper presents an improved ALGOL of "Lens". Based on the ALGOL and relative experiments, the characteristics of two kinds of field emitting cathodes are studied, With diameters of pinnacle 101 um. Coefficient of magnification of electronic fields gets to 102. The relationship between the intensity of static electric fields and the Structure of pinnacle are investigated. The influence of roughness of the surface of cathodes is analyzed. The ALGOL and computer program are applicable to nanometer cathodes with any shape.