With each unit cell replaced by finite cascaded massspring oscillators, 1D pho nonic crystals (PCs) can be simplified to an infinite periodic massspring chai n. Therefore, the elastic wave band structures of the 1D PCs can be calculated w ith a straightforward approach which we call lumpedmass method (LM). For compa rison, the band structures of the same 1D PC calculated with this method and the wellknown plane wave expansion method are both presented in this paper. The r esults of the two methods are in good agreement while the computation costs of L M method are much lower than that of PWE method.