Abstract Radial jet drilling technology is an economic and efficient method to enhance oil and gas recovery by drilling several lateral micro-holes from a vertical main borehole. The micro-holes drilled by high-pressure hydraulic energy can improve the contact area between wellbore and reservoir. The maximum extended reach of lateral micro-hole is a key parameter to evaluate the effect of radial jet drilling as the production increases with the length of lateral holes. However, the maximum extended reach of radial jet drilling reported has not been studied adequately. In this paper, we have established a new model which combines hydraulic friction and mechanical friction to analyze the extended reach of radial jet drilling. The results show that the flow rate is a main influence factor affecting the flexible hose extended reach which increases with the growth of flow rate. The outlet angle of deflector has a great effect on the extended reach especially at high flow rate, while the turning angle has little effect on extended reach. This work provides a systematic method including hydraulic and deflector optimization for the design of radial jet drilling to help develop the adjacent satellite oil & gas reservoirs.