Small-signal stability analysis of a power system needs the calculation of the rightmost eigenvalues of a system state matrix. The Block Arnoldi Chebyshev method (BACM) is used to calculate the rightmost eigenvalues, which is an improved version of the Arnoldi Chebyshev method (ACM). This method constructs an optimal ellipse containing unwanted eigenvalues and uses the Chebyshev iteration to acquire a restart matrix rich in basis vectors associated with the rightmost eigenvalues. Using the restart matrix including many more basis vectors, this method is good for calculating the clustered rightmost eigenvalues. The proposed algorithm is applied to the IEEE39 New England test system and the results of the experiment will be described.