Summary: In this paper, we analyze a multiscale method developed under the heterogeneous multiscale method (HMM) framework for numerical approximation of multiscale wave propagation problems in periodic media. In particular, we are interested in the long time \(O(\varepsilon^{-2})\) wave propagation, where \(\varepsilon\) represents the size of the microscopic variations in the media. In large time scales, the solutions of multiscale wave equations exhibit \(O(1)\) dispersive effects which are not observed in short time scales. A typical HMM has two main components: a macromodel and a micromodel. The macromodel is incomplete and lacks a set of local data. In the setting of multiscale partial differential equations, one has to solve for the full oscillatory problem over local microscopic domains of size \(\eta=O(\varepsilon)\) to upscale the parameter values which are missing in the macroscopic model. In this paper, we prove that if the microproblems are consistent with the macroscopic solutions, the HMM approximates the unknown parameter values in the macromodel up to any desired order of accuracy in terms of \(\varepsilon/\eta\).