A method to estimate the statistical properties of the wave groups in non-linear irregular waves is presented which is based on the Auto Regressive Model and the second order random wave theory. It is shown that the statistical problem of wave groups can be reduced to that of finding the Auto Regressive Coefficient and the marginal probability density function of wave amplitudes, from which the joint probability density function of successive wave amplitudes can be estimated. The method is verified based on numerical simulations and a field data measured in stormy sea states. It is shown that that there is good agreement between data and results estimated by the present method.