The single-molecule Raman detection has been realized for a long time because of the enhancement effect of surface plasmons. However, the small cross section of Raman optical activity (ROA) makes it so hard to detect the ROA of even a few molecules; and a normal surface-enhanced ROA (SE-ROA) is also very time consumable even with strong laser power. Detecting ROA in an economic way is an important issue. In this paper, we discuss the ultimate limit of the SE-ROA and provide the enhancement factor formula for SE-ROA. Following the formula, we proposed a structure with both huge Raman enhancement and ROA enhancement, which is helpful for single-molecule ROA detection.