Abstract
The classical Yang-Mills gravity with translation gauge symmetry in flat space-time was shown to be consistent with experiments in previous papers. We summarize the main features and then discuss the massless ghost particle and its interaction in pure gravity. It is convenient to formulate quantum Yang-Mills gravity by using the Lagrange multiplier method. We discuss the propagator and interactions of ghost vector particles. These results are necessary for the unitarity and gauge invariance of the S-matrix in quantum Yang-Mills gravity.