Unit commitment problem (UCP) is an essential concept in electricity generation due to various economical and environmental concerns. This paper presents a hierarchical combination algorithm for solving the UCP which is able to minimize the simulation time as well as the operational cost. Furthermore, the binary decision variables, determining the state of unit (on/off), are produced in each hour considering the demand and spinning reserve requirements (SRRs). Minimum up and down time constraints are applied in order to reduce the solution space. Finally, the economic dispatch (ED) is carried out for the feasible commitments obtained in each interval respect to the power generation limitations. In addition, the Priority List (PL) and Exhaustive Enumeration (EE) methods are implemented during the load increases and decreases, respectively. The proposed method has been implemented and applied to the standard power systems and the obtained results verify the relevant acceptable computational time with the optimal cost compared to the other well-known methods in the literature.