Unknown parameters of a modified crack growth model of float glass were determined. The crack length was assumed to follow four distributions. After selecting one distribution from four, the failure time of glass planes were simulated using different crack density and maximum crack length. Compare simulated and experimental results, the most appropriate crack density and the most appropriate maximum crack length were achieved. Four distributions combine with the corresponding crack density and the corresponding maximum crack length were used to simulated the failure stress. Compare simulated results of four distributions and experimental, the most appropriate distribution of crack length was determinate. The comparison was made between the simulation results and the former model, it was shown that this modified crack model can simulate the failure stress and the failure time accurately. The modified failure model with determinate parameters was used to predict the failure time of glass planes under blast loading. The simulation results are in good agreement with the experimental.