Inverse-designed digital nanophotonic devices have been widely and successfully used due to their simple brute-force design methods, compact footprint, flexibly-designed functions and high performance in various applications. Unfortunately, the number of 3D FDTD simulations in brute-force methods will increase exponentially with the “pixel” number in a digital pattern, which may drastically limit the inverse design capability of digital nanophotonic devices. In this work, we propose and demonstrate a modified adjoint method for efficient inverse design of compact digital nanophotonic power dividers with arbitrary power ratios.