A package structure and a formation method of a package structure are provided. The package structure includes a circuit substrate and a die package bonded to the circuit substrate through bonding structures. The package structure also includes a reinforcing structure over the circuit substrate. The reinforcing structure partially surrounds a corner of the die package. The package structure further includes an underfill structure surrounding the bonding structure. The underfill structure wraps around an end of the reinforcing structure. In a top view of the package structure, the reinforcing structure has an outer corner, and the underfill structure is spaced apart from the outer corner of the reinforcing structure.