Recently, four new platelet alloantigen (HPA) systems HPA‐18w to‐21w were identified. However, genotyping for HPA‐18w to ‐21w alleles was rarely reported. Here, we established a polymerase chain reaction sequence–based typing (PCR‐SBT) method and investigated the distribution of HPA‐18w to ‐21w alleles in the Chinese Han population. The specific primers of HPA‐18w, ‐19w, ‐20w and ‐21w were designed, and the PCR products were bidirectionally sequenced. 855 randomly selected platelet donors were genotyped for HPA‐18w to ‐21w with the PCR‐SBT method. The results showed that all individuals were monomorphic for HPA‐18w to HPA‐20w with a/a homozygous frequency of 1.0 and absence of HPA‐18bw to ‐20bw alleles. The frequencies of the HPA‐21a/21a and HPA‐21a/21b genotypes were 0.981(839/855) and 0.019(16/855), respectively. Seven mutations were confirmed on sequenced region separate from HPA polymorphisms, including ITGA2 (IVS17+48G>A and IVS17+72G>A), ITGA2B (IVS19‐26C>G) and ITGB3 (IVS4+234C>T, IVS11‐19 T>C, IVS11‐104T>C and GT repeats from IVS11‐131 to IVS11‐109). These data will provide useful information for diagnosis, prevention and treatment of alloimmune thrombocytopaenia.