Legged mobile manipulators are receiving much more attention. Mobile platforms can infinitely expand the workspace of robotic arms, providing more possibilities for robot application scenarios. Compared with wheeled mobile manipulators, legged mobile manipulators have higher requirements for cooperative control of legged robots and robotic arms. This work decouples the control of the robotic arm and the legged robot. On the legged robot side, we explicitly estimate the wrench exerted by the robotic arm on the base and bring it into the legged robot’s dynamics, and then use a nonlinear model predictive controller (NMPC) to control the legged robot. On the robotics arm side, we adopt an impedance controller to realize the end-effector’s force control, and the introduction of impedance control has improved the safety and interactivity of legged mobile manipulators. We conducted experiments on physical robot to compare the differences between decoupled control and independent control, and the results show that the stability and robustness of robot systems have improved using decoupled control.