The invention provides an observation method of an evolution rule of a strain localization band interval with a stress or strain. The method comprises: a digital image of a testing sample during a loading process is obtained by using a shooting device; a strain field with high smoothness is obtained by using a sub-pixel digital image correlation method and a bicubic spline interpolation method; strain data of each tested strain localization band are obtained; an initial value of iteration is set and one more dimension of any initial value is set than the number of strain localization bands, synchronous iteration is carried out continuously by using a swarm intelligence algorithm to reduce deviation between data and test solutions of all strain localization bands gradually, and then a unique strain localization band angle and respective different intercepts are obtained; and an interval between any two adjacent strain localization bands is calculated based on a distance formula between two parallel lines. The method has the following beneficial effects: accuracy and uniqueness of a measurement result can be guaranteed; a strain localization band interval evolution rule can be obtained; and automatic batch high-efficiency measurement can be realized.