The loading condition on the wind turbine during operation is complex. Therefore, based on a wind turbine foundation reinforcement project in Weihai, a systematic monitoring method is proposed to evaluate the performance improvement effect of the reinforced foundation in combination with the field environment. From the construction stage to the operation stage, the tower strain, welding stud strain, and anchor cable axial force of the reinforced foundation are collected to study the stress response of the wind turbine reinforced foundation under different working conditions, conduct correlation analysis, and to explore the performance improvement effect and load transfer mechanism after foundation reinforcement. The results show that the stress response of each component in the reinforcement area has trend similarity and amplitude difference, and the stress improvement effect is obvious with a large safety margin. The reinforcement method changes the stress boundary of the structure by using outsourcing concrete and welding studs, increases the restraint stiffness of the bottom tower, redistributes the upper transferred load, shares the transferred shear force, and ensures the common deformation of the tower and concrete.The systematic monitoring and evaluation method based on this reinforcement scheme can effectively and timely assess the stress state of each component of the reinforcement system and ensure the safety of the subsequent wind turbine operation. The reinforcement scheme improves the stress state of the foundation, rock bolt and flange, and the overall mechanical performance of the foundation is guaranteed.