A　good　quality　bitumen　emulsion　is　a　key　prerequisite　for　a　bitumen　emulsion　material　with　good　performance.　However,　current　evaluation　methods　of　bitumen　emulsion　cannot　distinguish　the　quality　of　bitumen　emulsions　with　the　similar　grade　of　chemical　stability　but　different　bitumen　particles　size　distribution.　The　maximum　packing　fraction　of　bitumen　particles　(phi(m))　formed　during　drying,　which　affects　the　chemical　stability,　drying　process　and　film　properties　of　emulsion,　is　firstly　proposed　to　evaluate　the　quality　of　different　bitumen　emulsions.　Then,　the　mechanism　influencing　the　phi(m)　of　bitumen　emulsions　is　discussed.　Results　indicate　that　although　the　same　emulsifier　type　and　dosage　are　used　to　produce　bitumen　emulsions,　the　phi(m)　of　different　bitumen　emulsions　can　still　differ　greatly　if　their　particle　size　distributions　are　different.　The　phi(m)　of　bitumen　emulsion　is　related　to　the　motion　ability　of　bitumen　particles　in　emulsion　due　to　particle　Brownian　motion,　which　is　mainly　dominated　by　the　bitumen　particle　size　and　emulsion　viscosity.　The　smaller　bitumen　particle　size　and　emulsion　viscosity　can　lead　to　a　higher　phi(m).　Based　on　the　phi(m)　results　of　bitumen　emulsions,　an　empirical　prediction　model　relating　phi(m)　to　the　essential　properties　of　bitumen　emulsion　(bitumen　particle　size　and　emulsion　viscosity)　is　established.　The　empirical　model　can　give　a　good　quantitative　relation　of　phi(m)　with　the　two　essential　properties　of　bitumen　emulsion.　It　can　be　used　to　rapidly　judge　the　quality　of　bitumen　emulsion　and　help　to　quantitatively　understand　the　effect　of　bitumen　particle　size　and　emulsion　viscosity　on　the　quality　of　bitumen　emulsion.