The invention provides a multi-QF-PCR STR detection system for performing fast diagnosis on the numerical abnormality of chromosomes, which comprises A, B and C three groups of PCR systems, wherein detection loci of the group A comprise AMXY, D21S1433, D21S1411, D13S258, D21S1414, D21S1412, D21S1445 and 21q11.2; the detection loci of the group B comprise D18S535, D18S391, SRY, D18S51, D18S386, D13S742, D13S634 and D13S303; and the detection loci of the group C comprise AMXY, DXS1187, DXS8377, SRY, DXS6809, DXS981, DXS1053, D13S305 and D21S11. When used in prenatal diagnosis, the fast detection system with enough STR loci and high heterozygosis rate of the STR loci can greatly shorten diagnosis time and buy precious time for timely treatment for clinicians and is prenatal diagnosis means with extremely high practicability.