The invention provides an optical measurement method for a symmetrical linear strain rate field in an object plane. The method comprises steps: multiple measurement plane images of a measured object during a loaded process of the measured object are acquired, measurement images are selected, and the shooting time for each measurement image is acquired; the displacement field and the speed field of each measurement point in the measurement plane are calculated; with each measurement point as a vertex, an image area with the measurement point on the first measurement image is dispersed into a non-overlapping non-gap quadrilateral pixel block and is further subdivided into two non-overlapping non-gap triangular pixel blocks; geometric parameters of the two triangular pixel blocks in each quadrilateral pixel block and the speed of each vertex are calculated; the linear strain rates of the two triangular pixel blocks in each quadrilateral pixel block are calculated; and a symmetrical linear strain rate is acquired. Thus, the temporal and spatial distribution law for an area with a high strain rate value during a loaded object deformation failure process can be detected, the obtained measured ribbon-shaped linear strain rate field is smooth and continuous, and the strain rate field measurement precision is improved.