The design and manufacture for GGI are different and only several countries have the ability to produce it. Devising the feasible scheme for gravity gradiometer is the primary question.In this paper, a new type of GGI is designed using twelve accelerometers. First, the mathematical relationship between the accelerometer and GGI is derived and the method to separate the angular velocity and gravity gradient is disscussed. Second, the model of twelve-accelerometer gravity gradiometer is provided. Third, the estimation of angular velocity is analyzed when the GGI is installed in the form of strapdown or stabilized state. Finally, it is concluded that a new type of inertial navigation system using gravity gradiometers will be configured when it becomes possible to precisely measure gravity gradient.