Abstract: Along the southern margin of the Junggar Basin, there are many faults and anticlinal structures are obvious, so the distribution of ground stress is complicated and the direction of the principal stress varies greatly with the position, which is unbeneficial to the trajectory optimization of horizontal well and the design of drilling fluid density window. To this end, the influence of anticlinal structure on local stress is considered while the 3D ground stress field calculation model is established. The ground stress component calculated by the numerical method is more accurate than that obtained by the analytical method. And correspondingly, the drilling fluid density window calculated by the numerical method is more accurate than that obtained by the analytical method. In this paper, single-well measurement and single-well ground stress analysis were firstly carried out on Well Gaotan 1 in this block. Then, fine finite element modeling and calculation was performed on the 3D ground stress field in the target block, so as to obtain the numerical solution of the 3D ground stress field in the block. Finally, based on the distribution of the directional angle of the principal stress in the 3D ground stress field, the trajectory of horizontal well was optimized and the corresponding safety drilling fluid density window was calculated, so as to provide theoretical basis and accurate reference data for the optimized, safe and fast drilling in Gaoquan Block. In conclusion, the model for the trajectory optimization of horizontal well and the calculation of drilling fluid density window based on 3D ground stress is accurate and practical.