The signal decomposition is translated into optimization problem in the adaptive and sparsest time-frequency analysis (ASTFA) method, and the signal can be decomposed adaptively in the optimization.In order to research the ASTFA decomposition capability, based on the evaluation index of decomposition capacity (EIDC), this paper studied the effect of amplitude ratio, the frequency ratio and initial phase difference by using the decomposition model with the double harmonic component synthetic signal.And then, the ASTFA was compared with the Empirical Mode Decomposition (EMD) and Local Characteristic-scale Decomposition (LCD).The results show that the decomposition capacity of the ASTFA is not influenced by the amplitude ratio or the initial phase difference, and the decomposed ultimate frequency ratio is larger.The decomposition capacity of the ASTFA method has the obvious superiority.