Abstarct: Conventional mechanisms usually have revolute or prismatic joints in their structure, so that the kinematic and dynamic analysis of the joints is performed ideally and assuming the absence of clearance in them. But in reality, and baxsed on the radius difference between the contacting surfaces in the joint, there is always some clearance in the joints that can be a source of error. It is noteworthy that the presence of clearance during a long period of operation of the mechanism, the wear and corrosion caused by it will increase the amount of clearance and cause adverse effects in the functioning of the mechanism. Therefore, detecting the presence of clearance is one of the important factors in reducing loss and damage to the mechanism components. In this research, one of the non-linear health monitoring methods called of higher harmonic generation is used to detect joint clearance . In this method, by applying a single frequency sine wave to the slider-crank mechanism, the accelerations of the mechanism members are compared in two states with clearance and without clearance (ideal) in the frequency domain, and the presence of clearance in the joints is detected. The method used was applied on the mechanism with the size of the clearances of 100, 200, 300 and 1000 micrometers. Also, different values were considered for the amplitude and frequency of the input and the results of different modes were compared. The comparison of the results of the accelerations shows that the appropriate selection of the input amplitude and frequency is very important in detecting the presence of clearance in the joints; Because if the appropriate selection is not made, the magnitude of the accelerations related to the smaller clearances will increase and it will cause higher harmonic generation method, to not detect the clearance correctly. Also, to detect joint clearance, the Root Mean Square Error index in the frequency domain has been used as a quantitative measure.