The invention discloses a method for detecting roughness of etched side walls through capacitance changes. The technical process is added before the etching process is carried out on a functional area only, and design complexity of functional devices is prevented from being increased. The roughness of the side walls of the functional area is reflected through the capacitance changes of detection areas, errors caused by small sizes are reduced, operations such as fracture surfaces causing damage to the devices are avoided, and nondestructive detection on etched structures is achieved. The number of the detection areas is determined through sizes and varieties of etched windows of the functional area, the purpose of more accurately detecting the roughness of the etched side walls under different conditions is achieved, and meanwhile the roughness of the etched side walls under the different etching conditions can be detected in one step. The technical process is simple, mature technologies are adopted in the process, technical difficulty is low, implementation is easy and convenient, and operation is easy.