Supernovae of Type Ia (SNe Ia) are becoming more significant objects, which can be used as a standard candle to measure distances to remote galaxies － and hence to determine the expansion rate of the universe. The progress on theoretical and observational studies of Sne Ia has been reviewed. Spectroscopical and photometric evidence indicates that SNe Ia originate from the thermonuclear explosion caused by accreting carbon-oxgyen white dwarfs. However, the progenitor systems and the hydrodynamical models are still controversial. The peak luminosities of bluer SNe Ia are relatively homogeneous, which can be calibratred to be the best distance indicators beyond the Virgo Cluster. In recent years, much progress has been made in measuring the space-time.