The multijet bit is a critical component of radial horizontal drilling technology, which not only has to break the rocks but also produce forward, self-propelled force to the high-pressure hose. The influence of structural parameters and hydraulic parameters on the rock-breaking efficiency of multijet bits was studied. Results show that the greater the number of holes of the jet bit, the more round the form of the borehole will be. As the lateral orifice diffusion angle increases, the rock-breaking efficiency first increases and then decreases. The working principle of the multi jet bit was investigated and the mechanical control equations of the jet bit were established based on the momentum flux method. Furthermore, the impact of bottom hole pressure drop generated by a back jet on self-propelled force was also studied. From the experimental results, the flow rate, forward reverse flow ratio of the jet bit, and the wellbore diameter are primary factors influencing the self-propelled force. Under experimental conditions, the self-propelled force increases with the increase of flow rate. With the same flow rate, the self-propelled force increases when the forward reverse flow ratio decreases. The self-propelled force first increases and then decreases as the wellbore diameter increases. The self-propelled force ranges from 67.8 to 228.1 N.