As the size of remote sensing camera increases, higher precision, wider range and more intelligent process of focusing method design is required. This paper introduces an in-orbit camera focusing method designed to be used on focusing mechanism of secondary mirror for high resolution remote sensing camera. The design of focusing method includes 4 operating modes: conventional mode, technical mode, targeted mode and automatic mode. Conventional mode is used to search for the best focal plane at initial period, and adjust when out of focus at in-orbit period. This mode offers optional control methods of open-loop and closed-loop. Technical mode is used for large-angle swaying imaging to compensate the decline of modulation transfer function. Targeted mode is used for specified target imaging. Automatic mode is used to search for the best focal plane automatically. This design of focusing mechanism and focusing mode provide high precision, multiduty, intelligent focusing ability to remote sensing camera, and used in-orbit successfully.