Incoloy800H is a kind of corrosion-resistant Ni-Cr-Fe base alloy with wide application in industrial fields. Vertical continuous casting process was developed to replace conventional mould casting process to increase product rate and decrease energy consumption. However, seriously internal quality issues of the continuously cast Incoloy800H alloy have been revealed. In this work, the square billet of Incoloy800H alloy, whose cross-sectional size were 100 mm×100 mm, were successfully fabricated in vertical continuous casting process with and without electromagnetic field (EMF), and the solidification structure, TiN inclusion distribution and internal crack were investigated. The result showed, without EMF, the Incoloy800H alloy billet had some seriously internal quality issues like coarse column grains, internal cracks and large TiN inclusion. With EMF, The equiaxed grain ratio of Incoloy800H alloy billet increased from 2.45% to 41.45%, the equiaxed grain size decreased from 10.83 mm to 1.28 mm and internal cracks were eliminated. TiN is a kind of detrimental inclusion in Incoloy800H alloy billet, which can act as stress concentration sites to form cracking. Most of TiN inclusions were located at interdendritic area and formed into TiN cluster to block interdendritic feeding channel. The application of EMF reduced the number of TiN inclusion from 3.71×10^-4 μm^-2 to 1.59×10^-4 μm^-2 in the center of billet. Further analysis illustrated that the EMF can refine the equiaxed grain size, reduce the degree of element segregation and the number of large TiN inclusion, which can reduce the probability of the crack initiation and inhibit the formation of TiN cluster to enhance the interdendritic feeding, thereby remarkably reduce the internal crack in Incoloy800H alloy billet.