The damage parameters of internal explosion in closed field are analyzed by using the dimension analysis principle, and the scale similarity model for internal explosion in closed field is established based on the similarity theory in this paper. The internal explosion of the original model under incremental charges manner until structural damage and the scale model under critical charge of structure cracks with different scale coefficients values of 0.8, 0.6, 0.4, 0.2 and 0.1 respectively are simulated by LS-DYNA code. The results show that, when the structure size stays constant but the explosive quality is changed, the arrival time of shock wave on the wall obey to similarity law, and the shockwave overpressure obey to similarity law which considered separately and affected by one wall, two walls and three walls respectively, but the impulse is not subject to similarity law due to the influence of structural damage. The shockwave overpressure, scale pulse width and scale impulse on the wall between scale model and original model obey to similarity law when the scale coefficient is no less than 0.1, and the maximum relative error of shockwave overpressure, scale pulse width and scale impulse between scale model and original model are less than 3.3%, 4.96% and 5.1% respectively. As the scale coefficients decrease, the shockwave overpressure, scale pulse width and scale impulse on the wall show a discrete distribution and the similarity degree decreases gradually. So if the scale coefficients are within the scope of this study it is feasible to predict the damage effect of original model under internal explosion using the scale mode experiment.