The invention provides a detection system and a probability assessment method for chain explosion of a lithium ion battery pack. The probability assessment method comprises the following steps: (1) determining a relational expression of the explosion probability YT and temperature T of a single battery; (2) determining a relational expression of the explosion probability YN and deformation N of the single battery; (3) obtaining an expression of the total probability Y of the single battery under different temperatures and deformations according to step (1) and step (2); and (4) detecting the temperature and deformation of each single battery in the lithium ion battery pack, calculating the explosion probability of each single battery according to the expression of Y, and determining the chain explosion probability of the lithium ion battery pack to be the highest explosion probability of the single batteries. The detection system and the probability assessment method for chain explosion of the lithium ion battery pack can be used for detecting the real-time chain explosion probabilities of the lithium ion battery pack under different working conditions and clinical conditions for chain explosion reaction, thereby realizing pertinent safety prevention and control.