Abstract: Slim-hole well drilling not only costs less, it can also be used to revive old wells by sidetracking, making it a way of economic and effective development of oil fields. When drilling slim-hole wells, some problems, such as high annular pressure loss and difficulty in carrying drilled cuttings out of hole, need to be solved. In slim-hole well drilling in Dixi block, a new high efficiency drilling fluid was used. The rheology and hydraulic performance of the drilling fluid was designed for different intervals: turbulent flow was used to drill the formations on top of the Permian system. The low-shear-rate rheology of the drilling fluid can maintain the pump pressures below 24 MPa, and the inhibitive capacity and the density of the drilling fluid are two key factors for the stabilization of the borehole walls. In drilling the Carboniferous system, turbulent-laminar transition flow pattern was used to improve the gel strength of the mud, and helped maintain the pump pressures below 26 MPa. In this way the disturbing of the drilling fluid flow pattern to the borehole walls was minimized, the carrying capacity of the mud in the horizontal section was enhanced, and the ROP increased by 66.4%. Field application showed that this high efficiency drilling fluid has played a role in stabilizing borehole walls and increasing the ROP in the drilling operation in Dixi block.