The main purpose of this paper is to develop high-performance graphene-modified asphalt (GMA) and characterize graphene occurrence in asphalt and examine its mechanism. The main research methods are: Based on Lambert-Beer law and dispersants dipropylene glycol dimethyl ether (DME) and polyvinyl pyrrolidone (PVP), the absorbance of dilute graphene mother liquor (GML) solutions at different concentrations were obtained via ultraviolet/visible spectrophotometry, and the concentration of dilute GML solutions were obtained via supernatant algorithms. The absorbance and concentration of dilute GML solutions were fitted via regression, which obtained the absorbance coefficient. Then, based on nominal graphene dosage (G) and dispersant and graphene proportion (D/G), respectively, the absorbance coefficients were fitted via regression to establish mathematical GML materials composition models which were solved via First Optimization (1stOpt) analysis software. Following the materials composition, DME-GMA and PVP-GMA was prepared, and the corresponding performance tests were carried out, and GMA was characterized via metallographic microscope and micro/nano-CT scanning to explore the morphology of graphene and mechanism in asphalt. The results are: Based on dispersants DME and PVP, respectively, the materials composition are G = 0.53%, D/G = 160%, and G = 0.26%, D/G = 190%. The penetration, non-recoverable creep compliance at 0.1 kPa and 3.2 kPa of DME-GMA and PVP-GMA (based on matrix asphalt) were decreased by 7.44 and 7.76%, 20.82 and 30.95% (0.1 kPa), and 8.63 and 18.88% (3.2 kPa), respectively. The softening point, maximum force at 5 °C, ductility at 5 °C, fracture energy at 5 °C, antirutting factors at 64 °C, and creep recovery rate at 0.1 kPa and 3.2 kPa were increased by 4.57 and 7.17%, 41.96 and 61.29%, 14.91 and 18.30%, 55.51 and 98.81%, 17.26 and 40.51%, 646.77 and 867.88% (0.1 kPa), and 128.62 and 153.53% (3.2 kPa), respectively. The high- and low-temperature stability of GMA are notably improved via uniformly dispersing graphene in asphalt materials, and graphene occurs as agglomerates in asphalt materials, and dispersants DME and PVP increase the graphene agglomerate dispersion effect in asphalt materials, changing its larger, irregular morphology to a smaller, regular one. The better the graphene dispersion effect is, the better the GMA performance is. PVP-GMA attains a better performance than DME-GMA.