There are many uncertain risk factors that affect the urban power load and interact with one another， forming a complex risk system. It is of great significance for urban grid planning to study the structure of the risk system and the relationship between these risk factors， and clarify their influence on the urban power load. By taking the urban power load risk system as the research object， the urban power load risk factors are analyzed and the layered structure diagram and transport chain of risk factors are constructed with the interpretative structure modeling（ISM）. An urban power load forecasting model based on ISM risk analysis is proposed. The results of the case study of Beijing during the period 2001～2008 show that the method can effectively improve urban power load forecasting and provide a decision-making basis for urban load forecasting risk management.