The invention discloses an anti-floating control method suitable for a sandy stratum shield upwards crossing an existing large-diameter tunnel. The method comprises the steps that before shield upwardcrossing construction, engineering geology and environment in a specified range are surveyed, finite element numerical calculation is adopted for conducting prior three-dimensional simulation on deformation of an existing large-diameter tunnel structure caused by shield upward crossing construction, feasibility of an implementation method is judged, and deformation control indexes of the existinglarge-diameter tunnel structure are determined; in the shield upward-crossing construction process, real-time monitoring and feedback control are conducted on all indexes in the deformation control indexes to guarantee that the whole process of shield upward-crossing construction of an existing large-diameter tunnel structure meets all the indexes; and after the shield upward crossing construction is completed, the existing large-diameter tunnel structure continues to be subjected to upward floating monitoring and early warning. According to the invention, construction methods, parameter selection principles and various key technical parameters of three stages before, during and after crossing construction are comprehensively controlled.