Modal analysis helps us to determine modal frequency (ω), damping (ζ) and mode shape (ϕ) for each mode of structures. This information helps us to diagnose and provide a solution to the cause of the vibration that caused the problem. Tests such as impact test or even Operative Deflection Shape (ODS), only give us an idea of ​​how the structure vibrates; But modal analysis gives us a complete understanding of the mode shapes. In the Experimental Modal Analysis (EMA), it is necessary that the excitation force and the response of the structure are measured and the modal model of the structure is extracted. For this reason, researchers have proposed a new method called Operational Modal Analysis (OMA) to extract the dynamic characteristics of systems where it is not possible to measure the input force. OMA is a technique to identify the modal parameters of a structure under operating conditions. This technique is used for very large structures that cannot be excite effectively to receive a suitable response, or rotating equipment that cannot be turned off and stopped completely. Unlike building structures, the forces on mechanical structures are much more complex because they are a combination of harmonic components, and special attention should be paid to identifying and separating harmonic components from the real mode of the structure and removing the influence of harmonic components in the process of extracting modal parameters. In this article, various operational modal analysis algorithms are investigated for extracting the modal parameters of a single-ended beam involved in the presence of harmonic excitation. First, the tested beam is subjected to experimental modal test and system parameters are extracted. Then operational modal analysis is performed in the presence of harmonic excitation with different frequencies and modal parameters are extracted and compared with the experimental modal analysis results.