Coal gangue (CG) and coal fly ash (FA) are the main coal by-product wastes. This paper focuses on the pore structure evaluation of CG and FA blended cementing composites with various replacement levels from 3 days up to 180 days. Results indicate that negative effect of coal by-products on the compressive strength and average pore size can be reduced to a negligible level at late ages. Similar average pore size (similar to 10 nm) and critical width (10-20 nm) are found for CG and FA composites after 90 days. Moreover, the blended composites have significantly higher gel pore fraction, and the higher the dosage the larger the gel pore fraction. Multi-fractal feature is observed with the fact that scale of micro-fractal region is found always broader than the macro-fractal region and the micro-D-s is found always larger than the macro-D-s. Both the micro- and macro-D-s of blended composites are systematically larger than the plain pastes.