[Objective] The aim was to diagnose and treat dairy cow with Theileria annulata disease in a dairy farm. [Method] The epidemiological investigation,clinical observation, blood smear and PCR detection methods were used to diagnose the Theileria annulata disease in the diseased milk of a dairy farm in Xianghe County. [Results] The incidence rate of the epidemic was 31.25 %,and the mortality rate was 20.00 %. Ticks are distributed in many parts of the skin of diseased cows. The main clinical manifestations include fever,anemia,emaciation and surface lymphadenopathy. Microscopic examination showed that the edge of red blood cells was angular, and the cells were filled with parasites. The parasites were mostly located at the edge of red blood cells,which were oval,annular and pear-shaped. The specific primer F / R was used to amplify the extracted DNA by PCR, and a 750 bp amplified band was obtained. The epidemic was caused by the infection of Theileria annulata. The combination of Chinese and Western medicine was adopted to effectively control the spread of the epidemic. [Conclusion] Early detection,early treatment,elimination of ticks,maintaining environmental hygiene,effectively cutting off its transmission route and curbing the development of the epidemic should be carried out.