Confocal laser scanning microscope(CLSM) was used to observe the solidification behavior of Nickel-based single crystal superalloy CMSX-4 in real time. SEM and EDS were used to study the micromorphology and element segregation characteristics of the solidified samples. Shrinkage and carbide formation were observed during alloy solidification. There are three types of shrinkages: square shrinkages, pentagonal star shrinkages and angular shrinkages. The formation mechanism of the three shrinkages is disccused, which is mainly related to the shape of the enclosed area surrounded by the secondary dendrite arms growing in different directions. In addition, carbides are found to be composed of two forms, namely flocculent carbide and lath carbide. Hf elements are enriched in flocculent carbides, while Cr elements are enriched in lath carbides.