Based on near-infrared continuous-wave diode lasers, a rapidly swept cavity ringdown spectrometer was developed. By rapidly sweeping the cavity length based on a PZT transducer, the longitude mode between the laser source and cavity was matched and dis-matched. Thus, the optical signal inside cavity finished its ring down and the measurement of the ring-down rate. The experiments show that not only the significant advantage in sensitivity achieve 10-9 cm-1 , but also the great stable and reliable performances of the spectrometer. The quantitative capability of the instrument was also demonstrated by measuring the absorption spectroscopy of CH4 around 1653.72 nm. The instrument was used to monitor the concentration changes of ambient CH4 by measuring the absorbing peak value with a fixed wavelength source.