To study the explosion risk of thermal-runaway gas of ternary lithium-ion batteries, an experimental platform for the thermal-runaway gas explosion of lithium batteries was independently built. Based on the risk assessment theory, the safety of lithium batteries in different states-of-charge (SOHs) was quantitatively evaluated. The probability of thermal-runaway gas explosion was represented by the product of the ignition parameters of lithium batteries and the risk degree of gas explosion, the result of gas explosion was characterized by the explosion severity, and the risk of thermal-runaway gas explosion was evaluated comprehensively through experiments. Experimental results show that the battery with a high SOC is more likely to cause thermal runaway in a more intense manner, its thermal-runaway gas explosion range is wider, and the corresponding risk degree is greater. Within the explosion limit, the batteries with higher SOCs at the same location have higher risks. With an increase in the thermal-runaway gas concentration in the mixed gas produced by batteries with different SOCs, all the maximum explosion temperature, maximum pressure, maximum pressure rise rate and explosion risk show a changing rule of first increasing and then decreasing, and the parameters reach their maximums near the middle value between the upper and lower explosion concentrations.