Abstract: To solve the severe agglomeration problem of graphene in the metal matrix, leading to the poor mechanical properties of the composite materials, the organic solvent polyether amine (PEA) was used for the in-situ surface modification of graphene oxide nanosheets (GONs) to synthesize the graphene oxide monomers (GOMs). The Ti–6Al–4V (TC4) based composites (GONs/TC4 and GOMs/TC4) were fabricated via ultrasonic stirring and spark plasma sintering. The influence of GONs and GOMs on the microstructure and mechanical properties of the TC4 matrix was investigated, and the fracture behavior and strengthening mechanisms of GOMs/TC4 composites were explored. The results indicate that, compared with the TC4 alloys, the matrix structure of GONs/TC4 composites becomes finer, and the layered structure of TiC particles is formed with length of about 15.0 μm. The matrix structure of the GOMs/TC4 composites is more refined, and the relative density of the composites is higher. TiC is distributed in the matrix in the form of equiaxed particles, indicating that the dispersion of GOMs in the TC4 matrix is significantly improved. The mechanical properties of the TC4-based composites are significantly improved by polyether amine. The tensile strength of the GOMs/TC4 composites reach 1054.0 MPa, which is 20.6% higher than that of the TC4 alloys and 6.0% higher than that of the GONs/TC4 composites. Moreover, the GOMs/TC4 composites still maintain the relatively high elongation after fracture (approximately 8.0%), and the fracture surface exhibits the ductile fracture characteristic. The main strengthening mechanisms of GOMs/TC4 composites are fine-grain strengthening and GOMs load transfer strengthening.