The invention relates to field of engineering geological exploration analysis and discloses a rock block stability fast evaluation method based on a three-dimensional outdoor scene and stereographic projection. According to the rock block stability fast evaluation method based on the three-dimensional outdoor scene and the stereographic projection, geological investigation personnel versatilely analyze blocks likely to slip conveniently and rapidly in the field environment, visually make an evaluation for a side slope stability state, and qualitatively analyze the stability situation after personnel excavate the side slope at the same time. The method comprises the steps of 1, collecting rock mass structure geological data information in an engineering area; 2, introducing the geological data information to a three-dimensional outdoor scene platform to form three-dimensional terrain; 3, determining a natural rock side slope to be analyzed; 4, in the range of the natural side slope, screening out all structural plane data information; 5, cutting blocks in the three-dimensional outdoor scene platform; 6, generating a side slope stability analysis report according to a polar stereographic projection method; 7, according to a construction scheme, inputting artificial side slope data; 8, according to the polar stereographic projection method, natural side slope data and artificial side slope data, generating a stability report.