In this study, we proposed a strategy that combines the fragment contribution corresponding states (FCCS) and free volume theory (FVT) method, namely FCCS-FVT, to calculate the viscosities of ionic liquids (ILs) covering a wide range of temperatures and pressures. In the method, the FCCS model was used to calculate the critical properties and densities of ILs, and then based on those values, the FVT model was applied to calculate the viscosities of ILs. The results indicated that the FCCS-FVT method shows high accuracy with 6.6% in average absolute relative deviation of total 2138 data points (25 ILs), which covers a wide range of temperatures (258.15-573 K) and pressures (0.06-300 MPa). Moreover, it is more convenient for the FCCS-FVT method to be applied for quick and accurate calculation of viscosities of ILs because it needs only three adjustable parameters.