The invention provides an optical measurement method of a strain localization band dilatancy angle. The method comprises the following steps of collecting images and acquiring a displacement and a strain of each measuring point in the images; determining areas which contain strain localization bands to be measured and are related to a measured area in the other images except for a first image; making the strain localization bands to be measured be horizontal or vertical; arranging one measuring line which is tangentially vertical to the rotated strain localization bands to be measured, establishing a rectangular coordinate system and arranging several measuring points on the measuring line, and acquiring a displacement of each measuring point on the measuring line and a correlation coefficient distribution curve; determining coordinates of two critical points related to the strain localization band to be measured on the measuring line and acquiring the displacements and strains of thetwo critical points under the rectangular coordinate system; calculating the displacements of two boundary points of the strain localization band to be measured on the measuring line under the rectangular coordinate system; and acquiring a dilatancy angle of the strain localization band to be measured. In the invention, reliability of boundary point displacement information can be guaranteed and the real dilatancy angle of the strain localization band to be measured is acquired.