Objective To explore the occurrence of diaphragmatic muscle fatigue(DMF) in children with pneumonia and its relationship with respiratory failure.Methods One hundred and twenty-six cases of pneumonia(pneumonia group) and 60 healthy children(healthy control group) were selected,and 2K-V1 type intelligence electric impedance respirograph was used to measure diaphragmatic function of the children in both groups to find if the ribcage-abdomen motion was synchronic and to calculate M levels.The abdomen impedance values as X-axis were calculated,which were regarded,and the chest impedance values as Y-axis were calcaulated,which described two-dimensional chart of ribcage-abdomen motion curve and the ? angle which was between connection of maximum X value to the smallest X value and the X-axis were calculated.According to the changes of chest-abdominal curve in one-dimensional chart and the changes of M value and ? angle,the degree of the diaphragmatic muscle fatigue was judged.Results There were 98 cases of DMF in the 126 children with pneumonia,and 68 cases of which were type Ⅰ DMF,and 30 cases were type Ⅱ DMF.One-dimensional chart showed contradictory chest-abdominal respiratory motional curve,and two-dimensional chart moved in a clockwise direction.M value was(46.1?8.4)%,? angle was(136.7?12.0) degrees in children with type Ⅰ DMF;One-dimensional chart showed that the peak value of chest-abdominal respiratory motional curve dislocates,and two-dimensional chart moved in a counter-clockwise direction.M value was(17.2 ? 3.2)%,? angle was(48.2 ? 9.5) degrees in children with type Ⅱ DMF;the control group had M value(4.3 ? 1.0)%,? angle was(31.7 ? 5.2) degree.There were significant differences in M value and ? angle between type Ⅰ DMF children,type Ⅱ DMF children and healthy children(Pa