The utility model provides the subassembly is strengthened to an automobile body side, and it includes first side reinforcing plate, interior center pillar, its hookup extremely first side reinforcingplate and the floor support that forms the automobile body lower part, and second side reinforcing plate, its hookup to first side reinforcing plate, interior center pillar and floor support to lowerpart formation close structure in the vehicle side. The automobile body performance of this structure through transmitting the impact load to the floor support and come improving the side upon impactto improve the security performance. In addition, this subassembly makes the quantity minimizing of necessary part to the low -cost equipment method of permission such as spot welding, thereby reduction in production cost and increase the marketability.