The modified nanoplasma model has been used to simulate the interaction of large Ar clusters with high intensity femtosecond laser pulses. The modified model has weakened the huge enhancement of electric field inside the clusters, thus provides a more reasonable explanation. The calculated mean kinetic energy of Ar ions is in good agreement with our previous experimental results. For further experimental work, it is the quantitative analysis of the variation of the mean kinetic energy and charge states of Ar ions exploded from the interactions with thecluster size and laser intensity.