To expound the necessity that space decompression sickness (SDCS) should be separated from altitude DCS, comparison was made between the features of space DCS and altitude DCS. The etiology and pathogenesis of the space DCS and altitude DCS were the same, but the features of the rules leading to their incidences (included influencing factors etc.) were different. For the convenience of getting better systemic and definite knowledge about SDCS, and making effective preventive plans and theoretical expositous, SDCS should be taken as an independent professional term.