Criminals who were sentenced to three years in prison usually had to serve three years. However, if the criminal met the conditions for a reduction of sentence, he could reduce his sentence according to the law and did not need to serve the full three-year sentence. The reduction of sentence could not exceed half of the sentence. The specific circumstances of the sentence reduction needed to be decided based on the individual's performance in the detention center and prison, as well as whether he had rendered meritorious service. Therefore, the duration of the three-year sentence was usually determined by the individual's situation. It was impossible to give a specific time.