Using　the　gravimetric　method　the　adsorption　characteristics　of　SAPO-34　zeolite　and　silica　gel　to　water　vapor　in　vacuum　condition　have　been　experimentally　studied.　Comparisons　of　the　result　in　vacuum　condition　to　the　result　in　moist　air　condition　were　carefully　conducted.　It　was　found　that　the　equilibrium　adsorption　concentration　of　the　two　materials　in　vacuum　condition　was　higher　than　the　equilibrium　concentration　in　moist　air　under　the　same　condition.　Also,　the　adsorption　time　to　reach　the　equilibrium　state　was　greatly　shortened　in　vacuum　cases.　The　maximum　time　shortening　was　up　to　48.1%　for　the　SAPO-34　zeolite　and　38.8%　for　the　silica　gel　as　compared　to　the　time　of　the　moist　air　cases.　With　an　anti-S　type　of　the　adsorption　isotherm　curve　the　concentration　change　of　the　SAPO-34　zeolite　was　insensitive　in　the　middle　pressure　range,　while　the　concentration　change　of　the　silica　gel　was　more　sensitive　in　the　middle　pressure　range　with　a　S　type　isotherm　curve.　The　existing　Freundlich　equation　and　S-B-K　equation　did　not　fit　well　the　adsorption　isotherm　of　the　SAPO-34　zeolite　and　the　silica　gel.　Therefore　novel　correlations　were　proposed　and　they　fitted　the　experimental　data　with　much　better　accuracy.