Video processing methods and apparatuses in a video encoding or decoding system for processing residual data of transform blocks. A current transform block in a video picture is divided into multiple sub-blocks, and each sub-block in the current transform block is entropy encoded or decoded using multiple sub-block coding passes. Each transform coefficient level in each sub-block is visited once according to a pre-defined scanning order in each sub-block coding pass. Two or more syntax elements associated with transform coefficient levels in the current transform block are aggregated and coded in one single sub-block coding pass. The video processing method is applied if the current transform block contains at least one non-zero transform coefficient level and the current transform block is coded in Transform Skip Mode (TSM) according to some embodiments.