The invention relates to a mobile robot, to be particular, a three-arm composite inspection robot mechanism. The robot mechanism comprises a front arm mechanism, a middle arm mechanism, a rear arm mechanism and an electric appliance box. Each of the front arm mechanism and the rear arm mechanism comprises a wheel claw mechanism, a pitching mechanism, a revolution mechanism and a wheel claw moving mechanism. Each wheel claw mechanism equipped with a locking wheel and a walking wheel is driven by the pitching mechanism to pitch and rotate and is driven by the revolution mechanism to revolve. The middle arm mechanism comprises a middle clamping claw mechanism, a middle lifting mechanism, a middle pitching mechanism and a middle moving mechanism. The middle clamping claw mechanism equipped with a left clamping claw and a right clamping claw is driven by the middle lifting mechanism to lift and is driven by the middle pitching mechanism to pitch and rotate. The front and rear arm mechanisms are driven by the wheel claw moving mechanisms respectively to move. The middle arm mechanism is driven by the middle moving mechanism to move. The wheel claw moving mechanisms and the middle moving mechanism are all arranged inside the electric appliance box. The robot mechanism can quickly cross barriers in different routes, so that the inspection process is safe and reliable.