To detect the content of Plasmodiophora brassicae (P. brassicae) resting spores in soil samples accurately, quickly and conveniently, a real-time fluorescent quantitative PCR was applied to detect the content of resting spores of P. brassicae in 42 soil samples which collected from Xiangshui township in Xiangtan county, Lukou town of Changsha county and Taohuajiang town of Taojiang county. The results showed that the number of resting spores per gram soil in 40 of 42 soil samples were between 2.76×104 to 4.37×106, in which the samples with resting spores ≥104/g soil all had clubroot occurrence while the 2 samples with 8.42×102 and 9.78×102 resting spores per gram soil didn’t have. Therefore, occurrence risk of the clubroot was large when the content of P. brassicae resting spores ≥104 /g soil.