The invention discloses a novel acoustic-emission ground-stress-field measuring technology based on a plane stress condition, which comprises the following concrete steps of: supposing that the vertical direction is a known principal stress direction sigmaZ, and obtaining the magnitude of a principal stress according to a formula sigmaZ=gammad; in the horizontal direction, sampling a rock sample in the two mutually vertical directions and the directions with included angle of 45 degrees with the two directions; and loading and recording data, analyzing to obtain a Kaiser point, computing the magnitudes and the directions of the two principal stresses in the horizontal direction according to a theoretical computing formula, and adding the supposed sigmaZ to realize the three-dimensional stress measurement of a ground stress. The novel acoustic-emission ground-stress-field measuring technology based on the plane stress condition is a novel ground-stress-field testing technology, can make up for the deficiency of a traditional testing method, simultaneously can greatly save the measuring consumption, has the advantages of strong operability, accurate measurement and the like, is combined with means, such as rock mass mechanical testing, numerical simulation analysis and the like, can supply a powerful scientific basis for geotechnical engineering design and is a brand-new and internationally-advanced ground-stress-field testing technology.