We demonstrate large self-deflection of both bright and dark screening photovoltaic solitons existing in LiNbO3 crystal under an external applied field with numerical method, and we also demonstrate that the self-deflection is not only connected with the acceptor concentration NA but also with the external applied field E0. Under the same E0, when NA is lower, the self-deflection is more obvious. Under the same NA, when E0 is higher, the self-deflection is more obvious. We also find that self-deflection of the bright screening spatial soliton and that of the dark one are different: the bright screening photovoltaic soliton deflects obviously; while only one side of the dark soliton deflects, its extreme value point and the other side almost do not deflect.