Abstract: During the course of drilling horizontal well with coiled tubing,cuttings easily settle on the low side of borehole to form cuttings bed due to action of gravity.The features in the coiled tubing drilling,such as small pumping rate and no rotation in drill string etc,have made hole cleaning efficiency very low.In view of this problem,considering the interphase slip velocity and particle flow influence based on the Eulerian coordinate system,a mixture drift model of cuttings carrying in a horizontal slim-hole was established,which uses Realize κ-ε turbulence model and the SIMPLEC algorithm for numerical calculation, and studied the effects on eccentric annular cuttings migration by flow rate,annular eccentricity,cuttings size,mud viscosity and hole angle,to determine distribution pattern of cuttings velocity and concentration in annular space under all conditions.The study shows that cuttings carrying efficiency will increase in coiled tubing drilling horizontal wells with the change of several factors,i.e.the increase of flow rate of drilling fluid,the decrease of annular eccentricity,decrease of cuttings size and well inclination,and the increase of mud viscosity.