Abstract: When the treatment levcls of wax crysial mnodifier in Crudes are higher than cerlain level, It will coxrystolize with wax ciysials, In ihe growth process, mixcd eocrystals will be surrounded by polarized molecular groups and the sgstems will fall into saturation. Therefore, the rheological belavior will change. But, if trealment levels are lowor than this, the viscusity and pour point will not significantly reduce. Occordingly, the author establishs a guideline of optimal initial treatment level which will be useful to make good choise of treatment level for a givea wax crystal modifier.