As the end effector of the micromanipulation system, the microgripper determines the success of the micromanipulation tasks. The parallelogram mechanism is usually used as the final amplification mechanism of the microgripper because of its parallel clamping characteristics. However, the parasitic displacement occurs during the rotation of the parallelogram mechanism. Based on this, this paper proposes a two-stage amplification asymmetric microgripper based on a symmetrical composite half-bridge mechanism driven by a piezoelectric actuator. The piezoelectric actuator is placed inside the mechanism and acts on the input ends of the compound half-bridge mechanism on the left and right sides, thereby driving the parallelogram mechanism to complete the clamping action. During operation, the output force of the left and right composite half-bridge mechanism serves as the input end of the parallelogram mechanism, ensuring equal force application on both sides. Based on the flexible beam theory and coordinate transformation method, the mechanical model of the mechanism is obtained. The performance of the microgripper is obtained by finite element analysis and experimental verification respectively. In terms of parallel clamping characteristics, the rotation angle of the output end of the parallelogram mechanism in the traditional microgripper is 2.1×10-4°, while in the proposed design, it is reduced to 1.15×10-4°. This corresponds to a 45.28% reduction in parasitic displacement along the desired motion direction, significantly improving parallel clamping performance. Regarding displacement amplification, the traditional microgripper has a magnification of 12.6, while the proposed microgripper achieves a magnification of 14.3, representing a 13.5% improvement in the displacement amplification performance of the output end. For the issue of parasitic displacement at the output end, the traditional microgripper exhibits a parasitic displacement of 30.7 nm, whereas the microgripper designed based on the symmetrical compound half-bridge mechanism in this study reduces this to 10.8 nm, corresponding to a 64.8% reduction. In conclusion, compared with the traditional microgripper, the microgripper presented in this paper demonstrates superior overall performance.