[Objective] To discuss the incidence of myocardial injury and variation of cardiac function of critical child patients by detecting cardiac troponin I (cTnI) in blood and cardiac function indexes. [Methods] ELISA was used to detect the cTnI in blood of 34 critical child patients, in the meantime, EF, FS, PFVA, PEVP were measured too. The correlation between cTnI and cardiac function was analyzed. The control group was consisted of 32 healthy children. [Results] The cTnI in blood of critical child patients was conspicuously higher than that of the control group(P0.01), and cardiac function was yet rather lower (P0.01). EF, FS, PFVA, PFVP all had a negative linear correlation with cTnI in blood. [Conclusion] By detecting the cTnI in blood, we can have an early diagnosis of myocardial injury and deterioration of cardiac function for an early-stage treatment and improving prognosis.