A close-loop chirp compensation system which consists of a simplified frequency-resolved optical gating (FROG) device and liquid crystal spatial light modulator (LC-SLM) is demonstrated. Femtosecond laser pusles are measured by using simplified frequency-resolved optical grating. The phase feedback signals derived from the simplified FROG control the LC-SLM to compensate the chirp of pulses. As a result, 74-fs transform-limited pulses are obtained from nonlinear fiber femtosecond laser amplifier.