The invention discloses a multi-joint mechanical arm. The multi-joint mechanical arm comprises arm rotating joints and arm lifting joints all of which are alternately arranged in the axis direction of the mechanical arm. Each arm rotating joint comprises a first reducer end and a first motor end, wherein a first end face, perpendicular to the axis direction, of the first reducer end is opposite to a first end face, perpendicular to the axis direction, of the first motor end, a center axis of the first reducer end and a center axis of the first motor end coincide with an axis, and the first reducer end and the first motor end are driven by an electric mechanism to relatively rotate around the corresponding center axes. Each arm lifting joint comprises a second reducer end and a second motor end, wherein a second end face, perpendicular to the axis direction, of the second reducer end is opposite to a second end face, perpendicular to the axis direction, of the second motor end, a center axis of the second reducer end and a center axis of the second motor end coincide with the axis, and the second reducer end and the second motor end are driven by the electric mechanism to relatively rotate around the corresponding center axes. Each first reducer end is fixedly connected with the nearest second reducer end, and each first motor end is fixedly connected with the nearest second motor end.