Systematic studies of the influences of several factors on the residual flux and the characteristics of residual flux occurrence in current transformers are conducted by computer simulations. The current transformer model is established using the electro-magnetic transient program ATP. Detailed simulation studies are performed for the resultant residual flux under the impact of several factors， including short-circuit current breaking time， short-circuit current and its aperiodic component， primary side time constant， power factor and impedance of load at the secondary-side. The characteristics of residual flux occurrence obtained by this work provide theoretical basis for inhibiting the residual flux.