A series of poly(styrene-co-octadecylmaleimide) with various imidization degrees as flow improvers for model waxy oils with asphaltenes were prepared through the reaction between octadecyl amine and poly(styrene-co-maleic anhydride) (SMA) with random and alterative structure. With a small amount of the designed flow improvers, the wax crystals became fewer, smaller, and more dispersed in the oils, asphaltene particles were better dispersed, and the crystallization temperature and yield stress were reduced considerably. Moreover, it had been found that the performance of the resultant flow improvers for the bituminous paraffin oils is significantly affected by the imidization degree and maleic anhydride content, which are evaluated in terms of the polarity.