Abstract: To evaluate the time domain accuracy of flutter simulations, three coupling methods, i.e., loose coupling method, improved loose coupling method and tight coupling method, are used to simulate Isogai Wing and AGARD 445.6 Wing models fluttering in the time domain. In analogy to the grid convergence analysis, a time accuracy analysis approach based on the generalized Richardson extrapolation method for time domain flutter simulations is proposed, with which the time convergence and accuracy analysis of flutter boundary simulations in the time domain is performed, and the time discretization independent result is obtained. The analysis shows that time domain simulation results of both Isogai Wing and AGARD 445.6 Wing flutter have good time convergence. The time accuracy obtained by generalized Richardson extrapolation method is basically consistent with that of the theoretical analysis. Within an appropriate time step range, the influence of time step selection for the analysis can be neglected. The present study suggests that it is feasible to establish a time accuracy analysis method based on the generalized Richardson extrapolation method for flutter simulations in the time domain.