To delineate a planar engagement scenario through mathematical expressions, the paper first establishes the connection between the desired line-of-sight and flight-path angle. Unlike conventional guidance laws that assume zero target maneuvering, which often results in significant impact angle errors, this approach employs an extended state observer to enhance tracking performance. Utilizing the error of angle, a sliding mode is devised to design the guidance law, with the stability of the proposed method validated through Lyapunov theory. The effectiveness and robustness of the method are demonstrated through numerical scenarios. This method offers precise estimation of target maneuvering and facilitates interception.