All-fiber-optic magnetic field sensor integrated with magnetic fluid has been investigated for decades, accompanied by the commitment to vectorization, miniaturization, integration and solving the temperature cross-sensitivity caused by thermo-optic effect of magnetic fluid. A kind of dual-channel-in-one temperature-compensated all-fiber-optic vector magnetic field sensor was proposed and investigated theoretically in this work. Three optical surfaces, including two sensing surfaces (plated with gold film of 40 nm thickness and then coated with magnetic fluid and polydimethylsiloxane, respectively, referred as CH1 and CH2) and one reflective surface, were integrated on a single-mode fiber tip to facilitate the dual-channel-in-one design. The Kretschmann configurations were formed by the waveguide fiber, gold film and functional materials at the sensing surfaces (CH1 and CH2). Surface plasmon resonance was excited in different wavelength bands corresponding to CH1 and CH2. Attenuation wavelengths corresponding to CH1 and CH2 depend on the magneto-induced and temperature-induced refractive index change of functional materials, respectively, which makes the temperature-compensated magnetic field sensing possible. The non-centrosymmetric evanescent field generated by micro-fiber-tip-prism enables the vector magnetic field sensing. Especially, the length of the sensing area is only 115.5 µm, which achieves ultra-integration and miniaturization. The current work provides a novel scheme for designing all-fiber-optic vector magnetic field sensing based on magnetic fluid and demonstrates the realization of lab-on-a-fiber and then promotes the industrial application of all-fiber-optic vector magnetic field sensing devices.