Nonsequential double ionization of He atom in the combined field of a laser and a static electric field has been investigated. It is found that the presence of the static electric field breaks the inversion and reflection symmetry, the symmetric double-peak structure of the He2+ ion momentum parallel to the polarization of the laser field is broken. Since the ultrashort laser pulse has the similar asymmetric character, this study is helpful to understand the mechanism of the double ionization process in ultrashort laser field.