The invention relates to an after-rolling cooling system for a hot rolled steel strip production line. A cooling device is provided with collecting pipes which have different densities and are arranged on a rolling line along the rolling operation direction of a steel plate sequentially. The after-rolling cooling system is characterized in that: a super fast cooling region and a laminar cooling region are arranged at the back of a rolling mill; the super fast cooling region has a dense pipe flow structure and is provided with two groups; the upper and lower collecting pipes are correspondingly arranged above and below each roller and are connected with high-pressure water pipes; the nozzle of each collecting pipe has an inclined injection-type gap structure; the number of the collecting pipe groups in the roughly cooling section of the laminar cooling region is 5 to 10; the number of the collecting pipe groups in the densely cooling section of the laminar cooling region is 5 to 10; the number of the collecting pipe groups in the finely cooling section of the laminar cooling region is 2 to 3; the lower collecting pipes in the laminar cooling section adopt sprayer nozzles which are formed in the gap of each roller way and are connected with normal-pressure water supply pipelines; sweeping devices are arranged in front of and at the back of each group of collecting pipes of the system; and side blowing devices are arranged on two sides of each roller way and are used for removing residual water on the surface of the steel plate. Cooling intensity is adjusted according to different parameters of products and rolling mills, so the requirement that the steel strip is quickly cooled from a temperature range of 800 to 1,000 DEG C after rolling to a temperature range of 200 to 750 DEG C can be met.