The determination of the critical breakdown path in slightly uneven electric field has played a significant role in gas discharge starting process and electrode surface erosion. In order to study the law of the critical path position in the low-pressure breakdown case, a new algorithm based on the Monte-Carlo collision model and the postulation of " forward-back trajectory for electrons” is established, namely the determination of the critical path(DCP) model. In the DCP model, some electric field lines among the electrodes are regarded as the potential breakdown paths, and the probability of the excitation and ionization collisions between the electrons and the neutrals can be obtained by the Monte-Carlo model. The most probable path to trigger the breakdown will be selected from among all the potential paths, namely the critical breakdown path, and the corresponding breakdown voltage of the critical path will be calculated. A breakdown test with two different electrode devices is performed to examine the accuracy of the DCP model: the critical path and breakdown voltage obtained by the DCP could be examined respectively by capturing the surface traces of negative electrode and measuring the breakdown voltage. According to the test results, the critical breakdown path can transit at different gap pressures or flow rates, and this observation is qualitatively consistent with the calculation results. Meanwhile, the relative error maximum of the breakdown voltage obtained by DCP is less than 7.9%. The accuracy of the DCP model partly depends on the background pressure, and the background pressure in the application case should be less than 103 Pa. Based on the DCP model, the numerical analyses of another four electrode devices are conducted to acquire the common law about the critical breakdown path. According to the calculation results, the transition zone has both a high frequency of critical path transition and a " fluctuant and similarly straight” breakdown voltage curve with the gap pressure or flow rate increasing, and the critical path transition direction follows the rule of " from longer paths to shorter paths”. Lastly, the inherent laws of those regulations about the critical path are revealed by the DCP model.