The non-contact detecting method of the pantograph and catenary (PAC) system has been the subject of many studies. However, there are only a few different types of research on the non-contact estimation method of the PAC system’s contact force. As a result, this study introduces a non-contact approach for measuring contact force between pantograph and catenary (PAC) using image processing and the Kalman Filter. A non-contact contact force of PAC detection method which simply requires the vertical displacement of the collection head is proposed. A PAC contact force identification method is built based on the improved Kalman Filter and the PAC dynamics model, which is used to obtain the vertical displacement of the pantograph’s collector head. Only the vertical displacement of the collector head as determined by image identification is used to estimate the contact force. It might assist with the engineering application of contact force online monitoring.