According to the basic principle of CWEOP (Continue Wave Electro-Optic Probing), we detect the distribution of the electric field of two types of GaAs/GaAlAs heterojuction lasers (the proton- bombed and the broad- area contact). The experimental results obtained at different areas and under different bias conditions reflect the characteristics of lasers such as carrier confinement, the change of the distribution of electric field corresponding to different bias currents and the distribution of electric field under negative bias.