A small-load control system and method for a large-load tester are disclosed. The system includes a small-load loading device and a small-load control system. The small-load loading device includes a spring loading mechanism connected to an upper clamping head of an actuator unit of the large-load tester, a test piece connected to the spring loading mechanism, and a small-load sensor connected to the test piece. The small-load sensor is mounted on a lower clamping head of the actuator unit of the large-load tester. The small-load control system includes a controller, an upper computer connected to the controller, analog input apparatuses and an analog output apparatus. Through a set of the outer small-load loading device and the control system, a displacement control function of the large-load tester is utilized to achieve accurate small load control. The small-load control system and method for the large-load tester are used for improving small load control precision of the large-load tester, broadening the application range and universality and reducing equipment investment.