It is well known that stars form in molecular clouds. Through almost 30 years’ observation and study, astronomers come to a relatively clear agreement that low mass stars form by collapse, accretion and outflow. However, for massive star formation there still exist many indefinite factors. The observational results show that maybe massive stars form by collapse, accretion and outflow either, without excluding the possibility that massive stars form by coalescence. Low mass star forming regions include only low mass stellar objects, but massive star forming regions include not only massive stars but also low mass stars. Massive stars are associated with UCHII regions well in their embedded phase. This paper summarizes the results of observation and study for star formation in different phases. Massive star formation and star formation in star clusters will be very important in the future work.