On the basis of review of recent advances on tracing ore forming fluid by using widely adopted δD vs δ18O system, attempt is made to discuss the reliability of δD vs δ18O system in tracing ore forming fluid of hydrothermal mineral deposits. The questions related to the problems were proposed. It is recommended that systematic analysis and effort on δD-δ18O from inclusion fluid in sulfide should be explored, coupled with minor volatile ratios and He-Ar isotope compositions, to trace the origin of ore forming fluid of hydrothermal ore deposits.