The invention relates to an on-line quenching and plate shape control process of wide and thick plate for water and electricity. According to the process, jet cooling on-line quenching is performed by using positive jetting, positive jetting and reverse jetting as one unit; in a jet impact region, cooling water and the surface of a steel plate perform heat exchange; meanwhile, most of cooling water is limited in the jet impact region using the positive jetting, positive jetting and reverse jetting as the unit. According to the thickness specification classification of the (wide) thick plate for water and electricity; the passing type cooling or swinging type cooling on-line quenching is selected; the maximum heat exchange efficiency of cooling water and the steel plate is realized; a good cooling plate shape is obtained. The process has the advantages that the temperature uniformity of an on-line quenching steel plate through plate is ensured; the off-line quenching of the (wide) thick plate for water and electricity is transplanted to on-line production; the production flow is simplified; the production cost is reduced; meanwhile, heat treatment production line resources are saved; the cargo supply period is shortened.