In this paper, we demonstrate a scheme to tailor both longitudinal and transverse modes inside a laser cavity and constitute an eye-safe single longitudinal mode $\mathrm{Er}:{\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ (Er:YAG) vector laser. A $q$-plate is employed as a spin-orbital conversion element to modulate the transverse mode and obtain cylindrical vector beams. An optical isolator is employed as a non-reciprocal element for the ring cavity to enforce unidirectional operation and achieve single longitudinal oscillation. The characteristics of power, transverse intensity, and polarization spectrum of the output beams are observed. The observed typical single longitudinal mode and highly matched special polarizations prove the successful tailoring of both longitudinal and transverse modes.