Cell microinjection is extremely crucial in biomedical domain. In this article, a new force-sensing cell microinjector with novel compliant small-stiffness mechanism is proposed. It enables both a high sensing sensitivity and large loading capability. The small-stiffness mechanism is realized by combining a constant-force mechanism and a small positive-stiffness mechanism with force intercept. The small positive-stiffness mechanism is adapted from the constant-force mechanism. The constant-force mechanism is used to eliminate the force intercept of the small positive-stiffness mechanism when the constant-force mechanism works at constant-force motion range. The constant-force mechanism is modeled, simulated, optimized, fabricated, and calibrated. Results show that the designed small-stiffness mechanism can remove the intercept force well. Based on the proposed mechanism, a force-sensing microinjector is designed and fabricated. Experimental results demonstrate the feasibility of the concept design of the new microinjector. Moreover, the microinjector is equipped with force-sensing ability by bonding two piezoresistive strain gauges, which provides 2σ resolution of 1.24 mN.