This study synthesized an imidazoline biosurfactant (IM-BioSurf) from biomass residue and tetraethylenepentamine in two steps. Its structure was characterized by Fourier transform infrared spectroscopy (FT-IR) and proton NMR spectra (1H-NMR). The critical micelle concentration (CMC) and surface tension (γCMC) of IM-BioSurf were measured, as well as the interfacial tension between the IM-BioSurf aqueous solution and asphalt. At 298 K, the CMC and γCMC of IM-BioSurf were 4.95 g/L and 38.27 mN·m−1, respectively. IM-BioSurf significantly reduced the oil-water interfacial tension, thus conferring excellent surface and interfacial activity. Emulsified asphalt prepared with the IM-BioSurf emulsifier had excellent storage stability and a uniform particle size distribution with an average size of 1.55 μm. In addition, the influence of IM-BioSurf on evaporation residue performance indicators was very small. Moreover, micro-surface tests showed that the emulsified asphalt acts as an excellent binder in asphalt mixtures. Most importantly, the biomass residue used to prepare IM-BioSurf can be readily obtained at low cost. As such, it is environmentally friendly, sustainable, and can greatly reduce the cost of emulsifier production. IM-BioSurf has broad application prospects as an asphalt emulsifier.