Objective To explore the relationship between minimal residual disease(MRD)on the 19th day(D19)and prognosis of children with acute B-lymphoblastic leukemia(B-ALL),as well as the correlation with related biological changes.Methods A total of 88 children with B-ALL newly diagnosed in this hospital from April 2016 to April 2020 who met the enrollment conditions were analyzed for induction therapy D19 MRD,overall survival(OS)rate,event-free survival(EFS)rate,chromosome karyotype,fusion gene and mu-tation gene.MRD≥ 0.01％was considered positive,and they were divided into MRD positive group and MRD negative group.The characteristics of OS rate,EFS rate,immunophenotype and molecular biology/cytogenet-ics were compared between the two groups over a period of 3 years.Results The 3-year OS rate and EFS rate of 88 pediatric patients were 92.0％and 86.4％,respectively.The rates of OS rate and EFS rate in MRD posi-tive group were lower than those in MRD negative group,with statistical significance(P＜0.05).The detec-tion rate of CD10 in MRD positive group was lower than that in MRD negative group,and the difference was statistically significant(P＜0.05).Thirty-two patients(36.4％)detected 8 types of 35 fusion genes.The de-tection rates of BCR-ABL1 and E2A-PBX1 in MRD positive group were higher than those in MRD negative group,and the differences were statistically significant(P＜0.05).Among 48 cases(54.5％)of pediatric pa-tients,41 types of 91 mutated genes were detected,and the remaining mutated genes were less than 5 cases.Abnormal karyotype was detected in 18 cases(20.5％),and no mitotic phase was detected in 17 cases.There was no difference in MRD between normal and abnormal karyotype.Binary Logistic regression analysis showed that BCR-ABL1 and E2A-PBX1 were prognostic factors of children with B-ALL.Conclusion The positive D19 MRD is the influential factor of adverse OS and EFS in children with B-ALL.Both E2A-PBX1 and BCR-ABL1 have adverse effects on the prognosis of children with B-ALL.