Hydraulic cavitation jet technology is widely used in petroleum drilling for its safety and reliabiligy with good effects. According to the conditions of poor drillability and low ROP in lower part of medium hard limestone formation of Y oil field in Iran, hydraulic cavitation jet tools are tested. By the study on the formation strength of test oil field and the drillability parameters, hydraulic pulsed cavitation jet device and BHA were selected; the mechanical and hydraulic parameters have been optimized. The real drilling data indicate the obvious improvement of hydraulic cavitation jet drilling tool, which is good for drilling in medium hard limestone formation.