By analysing the similarity between defense qi and leukocytes in terms of function， site of action， and circadian rhythm， it is proposed that in traditional Chinese medicine （TCM）， the pathogenesis of leukopenia is defense qi deficiency. By analyzing the relevant discussions on the generation and transmission of defense qi in TCM classics， it is believed that the original qi in lower jiao （焦） is the source of defense qi， while the water and grain qi in middle jiao enriches defense qi， and the upper jiao transmits and distributes defense qi to the whole body. Therefore， when treating leukopenia after chemotherapy with TCM， Guilu Erxian Gelatin （龟鹿二仙胶） and Yougui Pill （右归丸） are often used to tonify the kidney and supplement essence， and moxibustion at Guanyuan （CV 4） and Qihai （CV 6） is usually accompanied to replenish the original qi in lower jiao and enrich the source of defense qi. Guipi Decoction （归脾汤）， Buzhong Yiqi Decoction （补中益气汤）， Shenling Baizhu Powder （参苓白术散）， and Sijunzi Decoction （四君子汤） are often suggested to strengthen spleen and replenish qi， in combination with moxibustion at Zhongwan （CV 12） and Zusanli （ST 36） to transport the spleen and stomach in the middle jiao to enrich the defense qi. Modified Guizhi Decoction （桂枝汤） to harmonize nutrient and defensive aspects is often used， and moxibustion at Dazhui （GV 14） and Feishu （BL 13） or scraping is added to dredge the striae and interstice in the upper jiao and promote transmission and dissemination of the defense qi. Considering the whole process of generation and distribution of defense qi， it is suggested to choose the most appropriate treatment modality flexibly， and combine internal treatment with external treatment， in order to provide ideas for the treatment of leukopenia in tumour patients.