Abstract: The research had succeeded in detecting the Citrus Huanglongbing through the hand-sliced method or dot-marked observation by the monoclonal antibody with colloidal gold-labeled (MACG) technique. The methods are suitable for Citrus seedling detection of Huanglongbing pathogen in batch and general investigation in field, for they are rapidly and easily manipulated and low in price. By the MACG technique, we detected the Citrus plants in field, Citrus seedlings, their microbud-grafting plantlets and the plants after heat-therapy processed, the result showed that 6 kinds of Citrus plant in field, no matter the symptom of Huanglongbing pathogen was appeared or not, were detected to be infected by Huanglongbing pathogen. However microbud-grafting plantlets in tube and the seedlings, which grew from sterilized Citrus seeds, were Huanglongbing pathogen-free. Even most of the new branches and theirs-grafted plants which came from plants-infected after stable temperature processed for 30 days in 40℃ had no Huanglongbing pathogen.