The invention discloses a method and system for measuring the geometric density of a nuclear fuel pellet. The method comprises the following steps that the mass of the pellet to be detected is firstly obtained through a balance, then the boundary dimension of the pellet to be detected is measured, the volume of the pellet to be detected is calculated according to the boundary dimension of the pellet to be detected, and then the volume is divided by the mass to obtain the density of the pellet to be detected. According to the step of measuring the boundary dimension of the pellet to be detected, the diameter and height of the pellet to be detected are further measured. The method has the advantages of being high in measurement precision, high in measurement speed and the like. The system has the advantages of being simple and stable in structure, convenient to operate, high in disturbance resisting capacity, easy to maintain, accurate in locating, high in detecting precision, good in repeatability, wide in application range, beneficial for improving the measurement precision and the like.