Prestressed reinforcement is the key component of prestressed concrete structure, which is directly related to the safety, applicability and durability of prestressed concrete structure. In this paper, the corrosion degree of prestressed concrete is monitored by measuring the impedance between the prestressed reinforcement and the concrete reinforcement through a simple nondestructive testing method in post-tensioned prestressed concrete structures. The method has been tried in the 30-meter T-beam cross-sea bridge project, which makes a useful attempt for domestic popularization and application.