A data analysis system includes a modeling unit, a feature-extraction unit, a processing unit and an output unit. The modeling unit creates a prediction model by a machine learning algorithm according to training data. The feature-extraction unit extracts a plurality of fragment of feature data of input data, and classifies the feature data into a plurality of groups. The processing unit obtains a probability of the input data corresponding to the prediction model by the machine learning algorithm according to the feature of one of the groups, and determines the probability. When the probability is less than a predetermined value, the processing unit uses another feature data corresponding to another group which is not used to renew the probability of the input data corresponding to the prediction model through the machine learning algorithm. When the probability is greater than or equal to the predetermined value, the processing unit classifies the input data. The output unit outputs a classification result.