The invention relates to an online safety pre-warning method for a lithium-ion battery. The method comprises the following steps: determining an impact condition of the lithium-ion battery; determining a voltage change threshold of the battery; and carrying out online safety pre-warning of the battery. According to the method, the single battery with a potential safety hazard can be separated out by intercepting a voltage change value of the lithium-ion battery under a current or power impact condition within a certain period and carrying out transverse and longitudinal comparison on the numerical value, so that online safety pre-warning of the lithium-ion battery is achieved. Transverse comparison is carried out between different single batteries; and longitudinal comparison is numerical value comparison of various single batteries between different running time nodes.