Two-dimensional (2D) materials are an excellent platform for surface-enhanced Raman spectroscopy (SERS). However, a poor detection sensitivity hinders their practical application. Exciton resonance ( μ ex ) can improve SERS significantly by lending intensity to nearby charge-transfer resonance. Coincidentally, for ReS 2 , the enhanced μ ex can be achieved through the injection of excited-state electrons which can adjust the energy band to the SERS detection range. Moreover, ReS 2 has strong anisotropic properties, which adds an additional dimension for SERS. Therefore, ReS 2 is an ideal candidate to realize highly sensitive anisotropic SERS. In this paper, the metallic T phase of ReS 2 is introduced to the semiconducting Td phase by phase engineering. The photoinduced electron tunneling from the T phase to the Td phase can tune exciton emissions to the visible region, which effectively facilitates the photoinduced charge transfer processes. With RhB as the probe molecule, the synergistic resonance effects improve the limit of detection to 10 -9 M with the enhancement factor up to about 10 8 . Meanwhile, the obtained ultrasensitive SERS substrates also show good uniformity, stability as well as unique anisotropy. Our results open a new perspective in the improvement of the SERS performance.