Trenchless rehabilitation of underground pipes is increasingly important for city operation. A miniature robotic spraying system is developed to rehab buried pipes by remote spraying plural component protective coating to form lining on the original pipe inner wall. The system demonstrated three novelties, namely the remote mixing and spraying under low pressure, the long-range delivery of viscous coating using low pressure, and the hybrid hose step-down design, that make the system objective feasible. This letter presents the system setup and the remote rotary mixing and spraying mechanism. The mechanism is composed of a mixing chamber and a spray bit assembly. Half of the spray bit assembly with blade mixer feature stays in the mixing chamber for coating mixing, while the other half with rotary atomizer feature stays outside the chamber for spraying. Coatings are fed to the mixing chamber on ratio using low pressure and sprayed out by the high-speed rotation after mixing. The system setup and the mechanism are experimentally validated. The proposed method further opens the possibility of performing remote mixing and spraying over a long distance.