Study of interaction of explosive reactive armor (ERA) with shaped charge jet is the basis for evaluation of the effectiveness of ERA. The physically based theoretical model of this interaction is given. It is incorporated in the NERA computer code. The influences of backward moving plate and forward moving plate thickness, explosive layer thickness, jet attack angle, and distance between ERA and main armor are investigated. The comprehensive analysis of a longitudinal point of impact effect on ERA efficiency, based on NERA code calculations, is presented. Computational results of NERA code are compared with experimental data. The computational and experimental results of penetration in the steel armour target are in good agreement. The developed code enables optimization of explosive reactive armor characteristics.