Abstract: A jet mill bit (JMB) is proposed to increase the drilling efficiency and safety of horizontal wells, which has the hydraulic characteristics of depressurization and cuttings cleaning. This paper fills the gap in the hydraulic study of the JMB by focusing on the hydraulic modeling and optimization of the JMB and considering these two hydraulic characteristics. First, the hydraulic depressurization model and the hydraulic cuttings cleaning model of the JMB are developed respectively. In the models, the pressure ratio and efficiency are chosen as the evaluation parameters of the depressurization capacity of the JMB, and the jet hydraulic power and jet impact force are chosen as the evaluation parameters of cuttings cleaning capacity of the JMB. Second, based on the hydraulic models, the effects of model parameters [friction loss coefficient, target inclination angle, rate of penetration (ROP), flow ratio, and well depth] on the hydraulic performance of the JMB are investigated. The results show that an increase in the friction loss coefficient and target inclination angle cause a significant reduction in the hydraulic depressurization capacity, and the effect of ROP is negligible. The flow ratio is positively related to the hydraulic cuttings cleaning capacity, and the well depth determines the maximum hydraulic cuttings cleaning capacity. Finally, by combining the hydraulic depressurization model and hydraulic cuttings cleaning model, an optimization method of JMB hydraulics is proposed to simultaneously maximize the jet depressurization capacity and the cuttings cleaning capacity. According to the drilling parameters given, the optimal values of the drilling fluid flow rate, backward nozzle diameter, forward nozzle diameter, and throat diameter can be determined. Moreover, a case study is conducted to verify the effectiveness of the optimization method.