The firing model was studied to optimal design the bridge-belt electric initiating devices. Based on the non-Fourier heat conduction theory, the electro-thermal energy conversion model was established for the stage from heating to firing. And then the correlation of bridge-belt and input energy was obtained by MATLAB analysis. In order to verify its validity, the critical firing current experiments of Ni-Cr bridge-belts with two sizes were carried out by D-optimal method under the condition of 5 min current input and 50 ms current input. Comparison between the experimental and the analytical demonstrates that the model is reasonable and feasible for designing critical current of Ni-Cr bridge-belt, and the deviation between them is less than 14%.