The detection and discrimination of organic acids (OAs) is of great importance in the early diagnosis of specific diseases. In this study, we established an effective visual sensor array for the identification of OA. This is the first time, to our best knowledge, that metal ions were used to regulate the etching of silver triangular nanoprisms (AgTNPs) in an OA discrimination sensor array. The sensor array was based on the oxidation etching of AgTNPs by three metal ions (Mn2+, Pb2+, and Cr3+) and accelerated etching of AgTNPs by OA. The introduction of metal ions alone led to a slight wavelength shift of the AgTNPs colloid solution, signifying the incomplete etching of the AgTNPs. Nevertheless, when metal ions and OA were introduced simultaneously to the solution, a significant blueshift of the localized surface plasmon resonance peak was detected, and a color change of the AgTNPs was observed, which were the consequences of morphological transitions of the AgTNPs. The addition of different OA accelerated AgTNPs etching in varying degrees, generating diverse colorimetric response patterns (i.e., RGB variations) as "fingerprints" associated with each specific organic acid. Pattern recognition algorithms and neural network simulation were employed to further data analysis, indicating the outstanding discrimination capability of the provided array for eight OA at the 33 µM level. Moreover, excellent results of selective experiments as well as real samples tests demonstrate that our proposed method possesses great potential for practical applications.