Objective: To analyze the values of blood routine parameters in screening children with thalassemia (hereinafter referred to as “thalassemia”) gene carrier. Methods: Three hundred and fifty-eight children in Dongguan Children’s Hospital Affiliated to Guangdong Medical University from January 2019 to January 2020 were selected as research subjects, and their thalassemia gene was detected. According to whether they carried thalassemia gene, they were divided into a study group (80 cases with thalassemia gene) and a control group (278 cases without thalassemia gene). The basic data and the blood routine indexes between the children in the 2 groups were compared. Results: Among the tested children, 80 cases were diagnosed as carrying thalassemia gene, of which 48 cases carried α-thalassemia gene, accounting for 60%; most of them was --^SEA/αα type, accounting for 31.25%. Thirty cases carried β-thalassemia gene, accounting for 37.5%; most of them was CD41-42(-CTTT) mutation, accounting for 15%. Two cases carried α-thalassemia gene and β-thalassemia gene at the same time, accounting for 2.5%. The levels of red blood cell count (RBC), platelet count (PLT), and platelet distribution width (PDW) of the children in the study group were higher than those in the control group, and the levels of hemoglobin (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin content (MCH), and mean corpuscular hemoglobin concentration (MCHC) of the children in the study group were lower than those in the control group (all P<0.05). The results of receiver operating characteristic (ROC) curve analysis showed that the areas under ROC curve (AUC^ROC) of RBC, PLT, PDW, HGB, MCV, MCH, and MCHC in the screening of children with thalassemia gene was statistically significant (all P<0.05). Among them, the AUC^ROC of MCV was the highest, followed by MCH. Under the cutoff value, the sensitivity of MCV was the highest and the specificity of HGB was the highest. Conclusion: Children with thalassemia gene show abnormalities in a number of blood routine indexes. Among them, MCV, MCH have higher auxiliary diagnostic values. In population screening, we should comprehensively analyze the blood routine indexes of children, so as to improve the screening efficiency.