The widespread integration of flexible resources such as distributed photovoltaics, energy storage, and electric vehicles into low-voltage substations poses new challenges to the assessment of open capacity in substations. Therefore, an open capacity elastic interval evaluation method for low-voltage substation considering flexible resource regulation is proposed. Firstly, a mathematical model is established for the flexibility resources of the low-voltage substation and its adjustable potential is analyzed. Secondly, based on flexible resource optimal dispatch and considering uncertainty factors, an open capacity elastic interval evaluation model for low-voltage substation is constructed using information gap decision theory (IGDT). Finally, through simulations of different station areas, the open capacity elastic interval under various flexible resource combinations is analyzed from the perspectives of power supply and load access, and the effectiveness of the model is verified.