In this thesis we present the systematic analysis of narrow-line Seyfert 1 galaxies(NLS1s) in optical and X-ray observations. Narrow-line Seyfert 1 galaxies are a special subclass of AGNs, with the broad hydrogen Balmer lines less than 2000km/s and the relatively weak [OIII] lines; steep soft X-ray spectral slope and fast X-ray variability. Recently there are observational evidences that the NLS1s, which have the spectral similarities with blazar, also radiate in TeV. The most popular explanation is that NLS1s harbor small black hole masses and have relatively high accretion rate. Before our work, there are few research on the optical variability properties of NLS1s. However, the studies on this not only can help us understand their optical variability properties, but also can provide strong constraints on their physical explanations; We also can select the NLS1s with larger and rapid variability for reverberation mapping observations. And then derive their black hole mass measurements exactly. Zhou et al. (2006) select 2000 NLS1s from SDSS DR3，which enlarger the NLS1s, especially the objects with small emission line widths (FWHM(Hbeta) ~ 1000 km/s. Such NLS1s should have small black hole masses, and extreme X-ray properties, such as rapid variability and steeper X-ray spectra. However, these objects received less attention in the past than what they deserve due to their rareness.
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