A method for adding biometric authentication training data into databases performed by a biometric authentication data classification device includes: extracting first biometric characteristic information from at least one candidate biometric training data for biometric authentication using an artificial neural network model; calculating an overall similarity between the first biometric characteristic information and second biometric characteristic information extracted from a performance test database of which a biometric authentication performance is lower than a threshold level, the performance test database being selected among performance test databases for the biometric authentication; and adding the at least one candidate biometric training data into one of the biometric authentication training database and the performance test database based on the calculated overall similarity.