Abstract: OBJECTIVE To observe the association of lymphocyte subsets, oxygenation index (partial pressure of arterial oxygen/fraction of inspired oxygen, PaO₂/FiO₂) with treatment outcomes of the viral pneumonia (VP) patients complicated with acute respiratory distress syndrome (ARDS). METHODS Totally 65 VP patients complicated with ARDS whose treatment outcomes were death were retrospectively chosen as the death group, meanwhile, 65 patients whose treatment outcomes were survival were chosen as the surgical group. The clinical data were collected. Logistic regression analysis was performed for the influencing factors for the treatment outcomes of the VP patients complicated with ARDS. The association of CD₄⁺/CD₈⁺, CD₁₉⁺, CD₁₆⁺ ₅₆⁺ and PaO₂/FiO₂ with the treatment outcomes was analyzed by restricted cubic spline (RCS). The efficiencies of single and joint detection of CD₄⁺/CD₈⁺, CD₁₉⁺, CD₁₆⁺ ₅₆⁺ and PaO₂/FiO₂ in prediction of treatment outcomes were assessed by means of receiver operating characteristic (ROC) curves. The clinical practicability of the joint detection of the indexes was evaluated by decision curve analysis (DCA). RESULTS Logistic regression analysis indicated that the severity of ARDS(OR=6.406,95%CI:1.746 to 23.501)and mechanical ventilation duration (OR=1.210,95%CI:1.042 to 1.406) were the independent risk factors for the treatment outcomes of the VP patients complicated with ARDS; CD₄⁺/CD₈⁺(OR=0.042,95%CI:0.005 to 0.342), CD₁₉⁺(OR=0.739,95%CI:0.574 to 0.952), CD₁₆⁺ ₅₆⁺(OR=0.742,95%CI:0.575 to 0.956) and PaO₂/FiO₂(OR=0.976,95%CI:0.958 to 0.994) were independent protective factors (P＜0.05). RCS analysis revealed that there was dose-response relationship between CD₄⁺/CD₈⁺, CD_<sup>19⁺, CD₁₆⁺ ₅₆⁺, PaO₂/FiO₂ and the treatment outcomes of the VP patients complicated with ARDS. ROC analysis showed that the joint detection of CD₄⁺/CD₈⁺, CD₁₉⁺, CD₁₆⁺ ₅₆⁺ and PaO₂/FiO₂ had high value in prediction of treatment outcomes(AUC=0.900). DCA indicated that the probability of threshold value was 0.3 to 0.9, and the joint detection of the indexes had higher net profit in assessment of the treatment outcomes of the VP patients complicated with ARDS. CONCLUSIONS There is dose-response relationship between CD₄⁺/CD₈⁺, CD₁₉⁺, CD₁₆⁺ ₅₆⁺, PaO₂/FiO₂ and the treatment outcomes of the VP patients complicated with ARDS, and the value of the joint detection of the above indexes is highest in prediction of treatment outcomes.