Abstract: A new laser measuring system was developed to measure the radial displacement of triaxial specimens based on high precision PSD.In this system,direct measurement for the displacement of soil specimens with multi-points and non-contact method was carried out,which could measure change of diameters in several different positions at different time,meanwhile,a high precision of 0.009 mm could be reached through using the technique of laser & photoelectricity measurement and the principle of optical rigonometry during triaxial tests.Using this system,it could be likely to study stress and strain property of triaxial specimens in accordance with the actual condition.In addition,the main factors which would affect the precision and error of measurement were analyzed,and the precision of this system was validated through the measured results of the diameter of standard specimens.