A　theoretical　model　for　pore　size　estimation　of　mesoporous　materials　was　presented　in　this　paper.　It　is　based　on　the　statistical　thermodynamic　model　of　micelle　formation　proposed　by　R.　Nagarajan.　The　proposed　model　was　applied　to　predict　the　pore　size　of　MSU-X　molecular　sieve　prepared　in　different　synthetic　systems.　The　estimation　results　were　compared　with　reliable　experimental　measurements.　The　level　of　deviation　is　acceptable　with　the　substantial　simplifications　included　in　the　model.　Hansen　solubility　parameter　and　Dimroth-Reichardt　parameter　were　introduced　to　explain　the　discrepancies.　The　proposed　model　may　help　to　screen　suitable　synthesis　conditions　and　guide　the　controllable　synthesis　of　molecular　sieve　to　some　extent.