Developing high-performance flexible three-dimensional (3D) force sensors is critical for intelligent robots to perform precise manipulation in unstructured environments. However, the development of 3D force sensing is currently hindered by the low sensitivity, weak anti-interference capabilities, and limited pressure range of flexible pressure sensors. Here, we report a novel 3D iontronic force sensor (IFS) based on four ultrasensitive capacitance sensor units. By using the microstructured iontronic film as the sensitive layer, the IFS exhibits high sensitivity (2.08 kPa \(^{-1}\) ) under pressure from 0 to 1200 kPa, broad pressure range (0–2500 kPa) and high durability (over 3000 cycles). In addition, the IFS provides dynamic measurement of both the direction and intensity of forces with excellent signal decoupling capability. We have conducted a real-time grasping experiment using an IFS-based robotic gripper, demonstrating potential applications of robotic force feedback.