The signal transmission and processing is becoming faster and faster, and more and more problems occur during the high-speed circuit design. Signal Integrity is an engineering discipline that uses measurements, mathematics and simulation modeling techniques to ensure reliable electrical signaling between electronic devices. The crosstalk is one of the main issues of concern for signal integrity. The mechanism of crosstalk is introduced in this paper, and the simulation of crosstalk by ADS (Advanced Design System) is also given to analyze the method of reducing crosstalk.