Ca, Alrich inclusions (CAIs) are the earliest assemblages formed in the solar nebula. The formation models of CAIs include gas—soild condensation, crystallization from melting or partial melting and hightemperature evaporating residues. The latest study show similar distribution patterns of the petrographic types and sizes of CAIs in various chondrites. The petrographic characters argue that CAIs in various chemical groups of chondrites formed under similar processes and conditions probably in a same region in the solar nebula. This is consistent with previous studies of oxygen isotopes, Al—Mg isotopic system and rare earth elements, which suggest a same reservoir of CAIs in various chondrites.During and/or after formation, CAIs were transported into different locations where various groups of chondrites accreted.