In order to study the distribution of power frequency electric field in the substation whether the earth electrode of electrical equipment exists or not, the charge simulation method for the calculation of power frequency electric field in switch yard is derived in this paper. 500kV substation is taken for example, the switching yard and all kinds of the earth electrode of electrical equipment are modeled, and the power frequency electric field is calculated. First, numerical results are compared to measured, which verifies the correctness of the model; then analyzing the power frequency electric field distribution in switch yard whether the earth electrode of electrical equipment. This way provides an effective, efficient way for the calculation and analysis of the power frequency electric field with the existence of earth electrode.