The wavelet transform has been found very suitable for approximating steady-state waveforms of power electronics circuits. However, the time-domain piecewise property of power electronics circuits has not been fully exploited to maximize computational efficiency. In this paper, instead of applying one wavelet approximation to the whole period, several wavelet approximations are applied in a piecewise manner to fit the whole waveform. This new wavelet-based piecewise approximation approach can provide a very accurate and efficient solution, with much less number of wavelet terms, for approximating steady-state waveforms of power electronics circuits.