A safety prevention and control system of a power battery pack for an electric vehicle, comprising a battery pack for powering the electric vehicle, wherein the safety prevention and control system further comprises a signal acquisition device, a main controller, and a step-by-step prevention and control execution device; one end of the signal acquisition device is electrically connected to the battery pack, and the other end of the signal acquisition device is electrically connected to the main controller, for acquiring monitoring information of the battery pack, and transmitting the monitoring information to the main controller; the main controller comprises a fault diagnosis device, a cell thermal runaway determination device and a battery pack thermal runaway propagation determination device; the fault diagnosis device, the cell thermal runaway determination device and the battery pack thermal runaway propagation determination device are respectively electrically connected to the step-by-step prevention and control execution device, for sending a control instruction to the step-by-step prevention and control execution device; the step-by-step prevention and control execution device is configured to execute a prevention and control action according to the control instruction sent by the fault diagnosis device, the cell thermal runaway determination device, and the battery pack thermal runaway propagation determination device; wherein the fault diagnosis device comprises an internal short-circuit detector, an external short-circuit detector, a charge and discharge fault detector, an insulation failure detector, a collision detector, a liquid leakage and fire detector, and a superheat detector; the internal short-circuit detector, the external short-circuit detector, the charge and discharge fault detector, the insulation failure detector, the collision detector, the liquid leakage and fire detector and the superheat detector are respectively electrically connected to the signal acquisition device; the internal short-circuit detector, the external short-circuit detector, the charge and discharge fault detector, the insulation failure detector, the collision detector, the liquid leakage and fire detector and the superheat detector are respectively configured to concurrently diagnose different types of faults, determine the fault type, and send a control instruction with a fault level 1 targeting different fault types to the step-by-step prevention and control execution device; preferably, wherein the internal short-circuit detector comprises a processor, a selector, an electrochemical state determining device, a heat generation state determining device, and a logic operator; one end of the electrochemical state determining device and one end of the heat generation state determining device are respectively connected to the battery pack; the other end of the electrochemical state determining device and the other end of the heat generation state determining device are respectively connected to the processor; the electrochemical state determining device is configured to acquire the information of a battery having an extreme electrochemical state, perform model-based electrochemical abnormal state detection, and output a detection result of the electrochemical state of the battery; the heat generation state determining device is configured to acquire the information of a battery having an extreme heat generation state, perform model-based heat generation abnormal state detection, and output a detection result of the heat generation state of the battery; the processor is configured to store location and state information of the battery pack, and the processor is further configured to generate a control instruction for a prevention and control action; the selector is configured to screen an extreme battery based on an "average + difference" model; the logic operator is configured to perform a logic operation according to the detection results obtained by the electrochemical state determining device and the heat generation state determining device, and output an operation result to the processor.