JWL equation of state parameters for nitromethane (density of 1136 kg m-3) and two TNT explosives (densities of 1563 kg m-3 and 1602 kg m-3) were determined by means of the combination of hydrodynamically analytical method and cylinder expansion test. Cylinder expansion test not only laid much foundation for the analytical procedures to determine the JWL parameters of explosives but also provided a calibration standard for numerical calculations using JWL EOS. Through hydrodynamic and elastic - plastic - dynamic analysis on cylinder expansion movement, the isentropic pressures and specific volumes of detonation products might be related. The obtained pressure and specific volume data were then fitted by the isentropic form of JWL EOS to have the unknown parameters in JWL EOS be determined. Due to the fact that cylinder expansion test was unable to provide any information of detonation products at large volumes, we investigated several possible ways to take such situation into account and several sets of JWL parameters for each explosive were obtained individually. The obtained JWL EOSs were employed in the numerical calculations to reproduce cylinder expansion tests. Finally, a best set of JWL parameters for an explosive was found through comparisons of calculations and experiment.