This invention relates to a working device on an inclined surface, consisting of a working robot and a trailer that can run on an inclined surface, as well as a cable connecting the working robot and the trailer. There is a positioning system detects the relative position of the working robot and the trailer. The trailer can recognize the position of the working robot and autonomously move following the working robot. A power supply is installed on the trailer to supply continuous power to the working robot via the cable. The invention also covers a cleaning method for the solar panel array with the above-mentioned working device in a solar power station. The invention is characterized with low investment, easy installation and removal, operator-friendly management and maintenance.