Extinction Ratio (ER) is the essential parameter which evaluates the transmission performance of optical transmitter. Restrictions over ER also found in international standards. Calibration on ER parameter is primarily implemented through direct comparisons according to the standard ER source. But the critical step is to establish a stable, ER-adjustable optical signal source, which can generate high ER as possible. This paper has implemented a novel structure of high ER generator based on cascade Mach-Zender Modulator (MZM), which can generate data-rate-adjustable signal (12.5 Gb/s below), and maintain the output ER above 12dB.