Waxy crude oil containing large amounts of paraffins often results in various difficulties in extraction and transportation, especially at low temperature. Comb-type copolymers with phenyl pendants were found to be able to improve the flow ability of waxy oils effectively. To investigate the influence of spacer length between phenyl pendant and polymer backbone in comb copolymers on the flow ability of waxy oil, poly(alpha-octadecene-co-maleic acid phenyl alkyl amide)s with various spacer lengths were synthesized by modification of poly(alpha-octadecene-co-maleic anhydride) with aniline, phenethylamine, phentermine, and phenyl-undecanoicamide. Their effects on the morphology and crystallization of model and crude oils were observed by polarized light microscopy and DSC. The flow ability of both oils in the presence of copolymers was studied by means of rheology, including measuring yield stress, viscosity, and thixotropic properties. It is found that the spacer length remarkably affects the rheology and wax crystallization behaviors for both oils. The copolymer with a longer spacer can provide better flexibility of phenyl pendants to disperse asphaltenes more effectively, and the long spacer can cocrystallize with long-chain paraffins.