Abstract –This paper, presents the design and implementation of Frequency Modulation Continuous Wave (FMCW) radar system working at 77GHz for Adaptive Cruise Control (ACC) technology which is a flexible system to estimate the speed and distance in accordance to vehicle ahead, which reduces the forces on the rate of accidents by warning the driver when two vehicles become too close. In addition, the principle of FMCW radar is presented to generate Linear Frequency Modulated Continuous Wave (LFMCW) sweep waveform through frequency bands with triangular frequency modulation using Voltage Control Oscillator (VCO), a triangle sweep pattern adopt will resolve ambiguity without Doppler processing. This improves the decision making before hardware implementation. The simulation design is achieving the desired performance, one parameter warrants further attention. In the FMCW configuration, the sweep time is about 25 microseconds. Therefore, the system needs to sweep a 140 MHz band within a very short period. Such an automotive radar may able to meet the cost requirement.