In order to evaluate asphaltene dispersant effectively and accurately, the diluting viscosity alteration measurement method was carried out for the first time, and the defect of old precipitation method was analyzed combining with the evaluation results of commercially available dispersants. The effect of different groups, chain length and structure on the dispersion performance of dispersant was studied by the new method. The results showed that when precipitation method was used to measure the dispersant, alkyl benzene sulfonic acid and long chain ionic liquid with strong polarity caused serious concentration. According to a well?of?blending?diluting?oil in Tahe oilfield, the most suitable asphaltene dispersant was amine nonionic surfactant with C18 alkyl chain length and 2—4 polar groups. Based on this conclusion, a new type of long-chain alkyl amide asphaltene dispersant was synthesized by using oleic acid and diethylenetriamine. By diluting viscosity alteration measurement method, the average viscosity of dispersant and asphalt mixture was 890 and 277 mPa·s at 30℃ and 60℃ respectively, which increased 27% and 46% than that of commercial dispersant Span80.