A methods and apparatus for block partition in video encoding and decoding are disclosed. According to one method, a current data unit is partitioned into initial blocks using inferred splitting without split-syntax signalling. The initial blocks comprises multiple initial luma blocks and multiple initial chroma blocks, and size of the initial luma block is M×N, M and N are positive integers and the current data unit is larger than M×N for the luma component. A partition structure is determined for partitioning each initial luma block and each initial chroma block into one or more luma CUs (coding units) and one or more chroma CUs respectively. The luma syntaxes and the chroma syntaxes associated with one initial block in the current data unit are signalled or parsed, and then the luma syntaxes and the chroma syntaxes associated with one next initial block in the current data unit are signalled or parsed.