【Objective】 To investigate the influence of knowledge popularization concerning blood donation and blood use on the knowledge, attitudes and practice(KAP) of voluntary blood donation of patients′ families. 【Methods】 Knowledge popularization on voluntary blood donation and clinical blood use was conducted to family members of tumor patients. A questionnaire was designed according to KAP theory to capture the general situation, blood donation history and demographic characteristics of patients′ family members, their knowledge on blood donation and clinical blood use, as well as their intention, attitude and behavior changes on voluntary blood donation before and after popularization. 【Results】 13.49%(104/771) of the family members of tumor patients donated, and most of them aged 28~37 years old(19.7%, 26/132). The awareness rate of patients′ family members on voluntary blood donation and clinical blood use after popularizing was significantly increased as compared with before(P<0.05). Especially, the awareness rate of "blood transfusion significance and the risk of infectious diseases", and " patients were given priority to use blood if their family members donated blood" increased to 61.35%(473/771) and 68.74%(530/771), respectively.Their intention, attitude and behavior of blood donation also changed significantly(P<0.05). The intention of supporting voluntary blood donation increased to 78.21%(603/771), and non-supporting decreased to 4.15%(32/771). Such three behaviors led to a donation rate higher than 70% as donating for charity and sense of responsibility(74.06%, 571/771), donating blood after reassuring(70.69%, 545/771), and promoting their family members′ priority in blood use(71.47%, 551/771). 【Conclusion】 The popularization of knowledge concerning blood donation and blood use can change the intention and attitude of patients′ family members towards voluntary blood donation and further effectively promote their donation behavior.