The task of prison term prediction is to predict the term of penalty based on textual fact description for a certain type of criminal case. Recent advances in deep learning frameworks inspire us to propose a two-step method to address this problem. To obtain a better understanding and more specific representation of the legal texts, we summarize a judgment model according to relevant law articles and then apply it in the extraction of case feature from judgment documents. By formalizing prison term prediction as a regression problem, we adopt the linear regression model and the neural network model to train the prison term predictor. In experiments, we construct a real-world dataset of theft case judgment documents. Experimental results demonstrate that our method can effectively extract judgment-specific case features from textual fact descriptions. The best performance of the proposed predictor is obtained with a mean absolute error of 3.2087 months, and the accuracy of 72.54% and 90.01% at the error upper bounds of three and six months, respectively.