The invention relates to a baseline phase determination method and system for a foundation interometric radar in deformation monitoring. The method comprises the following steps: according to a pixelline number of an antenna center of the foundation interometric radar in a monitoring image during the deformation monitoring, determining projected amount of a baseline of the foundation interometricradar at each coordinate axis in a corresponding radar coordinate system during first deformation monitoring; and according to the projected amount of the baseline of the foundation interometric radar at each coordinate axis in the corresponding radar coordiante system during the first deformation monitoring, determining a baseline phase of the foundation interometric radar. The technical schemeprovided by the invention accurately calculates the baseline phase caused by position change of the foundation interometric radar during discontinous deformation monitoring, and then precision of a deformation monitoring result is improved.