Abstract: Many methods have been tried to solve the deflecting problem in highly steep structure,however with few successful under high WOB condition.The deflecting control mechanism of a novel articulate BHA under high WOB is determined,and its dynamic three bending moment equation,formula calculating the bit side force and bit deflection angle were also derivated;based on which,calculating and analyzing software was programmed.Two optimized BHAs were selected and tested in two wells in the highly steep structure of Chuandong area,with some useful knowledge obtained.