Various methods for pressure calibration by dropweight device are discussed in detail. The measurement accuracy of force sensor is easy to be influenced by pretightening force and inertia force. An improved method to enhance the measurement accuracy is proposed. A high precision force sensor is designed based on the structure of the original weight, from which the inertia force correction model of absolute calibration is derived. In further, the model simplification conditions are summarized. Calibration tests are carried out and the experimental results show that traditional installation methods of transition parts connecting and bolt fixing generate additional adverse effects of pretightening force and inertial force. As a result, relatively large error exists during the measurement of impact force between weight and piston rod. In contrast, pressure can be calculated directly by measuring values of force sensor and crosssectional area of piston rod, under the conditions that the mass of weight is far greater than piston rod and high precision of central impact. Compared with the existing quasistatic calibration method, the monitoring accuracy of high pressure is improved larger than 1%, which can be regarded as an effective pressure calibration method.