The DOAS technique is currently the developing trend and the main technique of online monitoring of tropospheric air quality measurements. In order to enlarge the scope of monitoring with only one set of instrument, we recently developed an multi-path LP-DOAS system in which we put several sets of retroreflectors at their own appointed remote places, each makes a measuring lightpath when the telescope aligns with it. In this way we can determine high spatial resolution and two or three-dimensional trace gas distributions of a larger region with the telescope as its center. We developed a stepping-motor-based mechanics-electrical device to drive the telescope. Under the control of a PC the telescope can automatically scan these retroreflectors one by one in continuous measure cycles.