Abstract: In recent years, diseased plants of citrus have been found in Yueyang County, Hunan Province. The symptoms of the diseased trees include leaf mottle, small fruit and stunting, serious whole wither. The symptom is similar to citrus Huanglongbing. In order to make a definite diagnosis of this disease, take the control measure in time, this research employed PCR technology detecting the disease. The PCR test results suggested that, Guanximiyou pomelos of Yueyang Huarong Nanshan County and Huarong Shenfeng County and Huarong Xihu County were infected by citrus Huanglongbing Pathogen. The Guanximiyou pomelos came from Hujian Province. In Chunfeng Garden Matang County, citrus topworked by Guangximiyou polemo was infected by citrus Huanglongbing Pathogen, but untopworked citrus reticulata Blanco cv. miyamoto was uninfected. Citrus from Yueyang was not infected by citrus Huanglongbing Pathogen. Citrus Huanglongbing pathogen was by detected from the citrus in Yueyang, that was the first discovered. Citrus Huanglongbing pathogen was from Guanximiyou pomelo of Hujian Province. Citrus Huanglongbing pathogen infect citrus by topworking and importing disease.A little citrus were infected by citrus Huanglongbing in Yueyang. Diseased citrus were Guanximiyou polemo from Fujian Province and citrus reticulata Blanco cv. miyamoto base stock, other citrus were not infected by citrus Huanglongbing pathogen in Yueyang.