This paper reports on the Raman tensor and selection rules of a chemical vapor transport (CVT)-grown CuGaSe2 single crystal. CVT-CuGaSe2 has a hollow needle-like shape with two flat faces of unequal area, (110) and (112), which involve different systems of coordinates. In order to study the Raman spectra of these systems, we probed the theory of Raman tensors and Raman selection rules. Using the MATLAB program, we calculated the Raman tensor of CuGaSe2 (D2d) and other point groups in different orthogonal systems. In addition, by applying the selection rules for Raman scattering to the observation of phonon modes from the (110) and (112) faces of CuGaSe2, we were able to assign the Raman modes at 187, 84 and 68 cm−1, which were in accord with the literature. Additionally, we found some new Raman modes.