A 1:1 matched case-control study was conducted to investigate the etiological factors of childhood leukemia. It was found that there were five risk factors: (1) children living in the environmental pollution area, OR (95% CI) = 2.84 (1.14-7.10); (2) exposure to extreme low frequency electronmagnetic field (ELF), OR (95% CI) = 2.01 (1.18-3.42); (3) history of postnatal X-ray exposure, OR (95% CI) = 4.53 (1.68-12.21); (4) history of taking chloramphenicol, OR (95% CI) = 3.60 (1.62-8.01); (5) history of taking, antipyretic or analgesic drugs, OR (95% CI) = 1.93 (1.09-3.42). A protective factor was also discovered. Mothers often eating fish, pork and other meat foods, OR (95% CI) = 0.33 (0.18-0.59). The analysis of the population attributable risk showed that 91% of the childhood leukemia cases might attribute to these five risk factors. The interaction among these etiological factors was estimated. Results showed that there was a positive interaction between the X-ray exposure and chloramphenicol on additive model, the relative excess risk due to interaction (RERI) of childhood leukemia was 3.04.