【Objective】To investigate the effect of human umbilical cord mesenchymal stem cells on infected state of human alve? olar type II epithelial cells.【Methods】Human alveolar type II epithelial cells A549（1×10 5 /mL）2 mL and PA（3×10 4 CFU/mL）2 mL has grown after 6 hours，add hUCMSC（1×10 6 /mL）2 mL as the experimental group，add equal amounts of phosphate buffer （PBS）for infection，A549 and PBS and the medium has grown as the control group. A549 cells morphological changes between the compared groups（Transmission electron microscope，TEM），A549 cell viability（new CCK-8 cell proliferation assay Kit），A549 cells apoptosis（Annexin V-FITC/PI double staining flow cytometry）and the expression of A549 pulmonary surfactant A（SP-A） （Western blot）. 【Results】Transmission electron microscope cell morphology observation displayed，infection group A549 cell dam? aged obviously，cell quality appeared empty bubble degeneration，chromatin height agglutination，visible apoptosis bodies；experi? ment group cell package film structure full，nuclear film full，nucleolus obviously，nuclear chromatin electronic density low，chroma?tin uniform，no apoptotic bodies；control group A549 cell structure full，membrane surface micro-fluff rich，nuclear film full，nucle? ar week clearance structure normal，chromatin uniform；infection group and control group compared，Infection group A549 cell sur? vival significantly reduced［（70.35±2.89）% and（97.37±2.07）%，n=3，P<0.01］，apoptosis rate significantly increased［（8.63%± 0.16）% and（2.55±0.11）%，n=3，P<0.01］，In the infected group，PA could damage A549 cells and decrease the amount of SP-A ex? pression（n=5，P<0.05）. In the experiment group，the protective effect of hUCMSC on the A549 cells after infection may increase the expression of SP-A（n=5，P<0.05）；【Conclusions】HUCMSC inhibits the infection of A549 cells apoptosis and protection of A549 cells secrete SP-A.