Abstract: Hydraulic-jet radial drilling technique is one stimulation measure with the characteristics of low cost and remarkable stimulation effect and it is widely applied in onshore oilfields. As for offshore oilfields, however, the operation cost is higher and longer horizontal sections are needed to improve stimulation effects. Reducing the frictional resistance in the interval of converter is one important method to increase the radial horizontal section length. the independently developed through-converter testing system was adopted to experimentally study the influential laws of converter’s structural parameters on through-converter frictional resistance. Then the influential degree of each structural parameter was analyzed by means of gray association analysis method. It is indicated that through-converter frictional resistance decreases as the internal corner, external corner and turning radius of the converter increase. The influential sensitivity of each parameter is ranked from the top the bottom as internal corner, turning radius and external corner of converter. Therefore, to design a converter, the priority shall be given to the reduction of internal rotation angle to reduce the through-converter frictional resistance, so as to increase the ultimate drilling length of horizontal section. The research results provide the reference for the future design of converter’s structural parameters and the application of this hydraulic-jet radial drilling technique in the Bohai Oilfield as soon as possible.