The invention relates to the field of molecular biology diagnosis, in particular to a detection kit for copy numbers of SMN1 and SMN2 genes. A seventh exon of SMN1, an eighth exon of SMN1, a seventh exon of SMN2 and an eighth exon of SMN2 are amplified simultaneously in a one-tube PRC reaction solution by using eight primers, meanwhile, one or two groups of housekeeping genes are used to monitor the PCR reaction efficiency, PCR products are analyzed by capillary electrophoresis and calculated according to an SMN normal control with 2 copy numbers of SMN1 and SMN2 genes, relatively quantitativedetection is performed on the cop numbers of the SMN1 and SMN2 genes, SMN1 and SMN2 genes with 0, 1, 2, 3 equal to or larger than 4 copy numbers are calculated, and SMA patients, carriers and normalpersons are distinguished. Results can be obtained within 3 h starting from DNA samples, the copy number conditions of the SMN1 and SMN2 genes can be detected only through one PCR experiment, the detection technical process is simple, and standardization is easy to realize.