The invention relates to a reinforced structure for a foundation with a wide defect and a construction method thereof. The invention aims to solve the technical problem of providing a reinforced structure with large span width and large bearing capacity for a foundation with a wide defect and a construction method thereof, so as to reduce the treatment difficulty, improve the bearing capacity of the foundation and reduce the foundation excavation and treatment work amount. To solve the problem, the invention has the technical scheme that the reinforced structure for the foundation with the wide defect is provided with a crushed zone, two sides of the crushed zone are stable bedrock, and a vertical arch style bearing body is arranged above the crushed zone. The construction method comprises the following steps: a, excavating in different positions; b, pouring concrete of an arch support; c, pouring the vertical arch style bearing body; d, carrying out curtain grouting, consolidation grouting, and mortar backfilling of the bottom of a basic structure body; and e, arranging a transition layer above the bearing body for leveling. The invention is mainly used for various hydraulic and hydro-power engineering.