The spinodal decomposition of symmetric and asymmetric binary alloys has been studied from precipitate evolution and coarsening mechanism by a binary phase field crystal method. The calculated results indicate that when the alloy composition changes from a symmetric point to the asymmetric one, the morphology of decomposed phases transforms gradually from long stripes to spheres, with the coarsening mechanism undergoing a transition from the coalescence of neighboring particles to Ostwald ripening. Only the coarsening kinetics of the binary alloys which is close to the spinodal decomposition line is in a fair agreement with the prediction of the modified LSW theory