Objective Based on the Chinese Diet Balance Index (DBI_22), this study comprehensively evaluated the dietary quality of adult residents in Guangdong Province from 2002 to 2022, aiming to identify long-term trends and existing deficiencies, and provide data support and theoretical guidance for implementing targeted nutritional interventions. Methods Data from four rounds of the Guangdong Provincial Nutrition and Health Monitoring Survey (2002-2022) were utilized, focusing on permanent adult residents aged 18 years and older. A multistage stratified cluster sampling approach was employed. Dietary data were collected using a 3-day 24-hour dietary recall method combined with weighing techniques. The DBI_22 was applied to calculate scores for various indicators, including positive-end score (HBS), negative-end score (LBS), and dietary quality distance (DQD). Data were weighted and analyzed using χ², Kruskal-Wallis H, or Jonckheere-Terpstra trend tests, with stratified comparisons by gender and urban/rural residence. Results During the study period, the overall dietary quality of adult residents in Guangdong Province remained persistently in a state of “moderate imbalance” (median DQD scores ranging from 36 to 41 points), characterized by concurrent “moderate deficiencies of intake” and “mild excesses of intake.” Severe deficiencies existed in vegetable/fruit, dairy, and soy product intakes (deficiency rates ranging from 77.23% to 89.46% and 95.61% to 99.07%), with limited improvement over two decades. While grain overconsumption decreased from 43.63% to 28.18%, deficiency rates rose to 17.40%. Animal food consumption patterns underwent significant shifts by transitioning from predominant deficiency (26.07% deficiency rate in 2002) to emerging excess (16.40% excess rate in 2022). Persistent issues include excessive intakes of pure energy foods and condiments and insufficient dietary diversity. Stratified analysis revealed significant urban-rural, gender, and socioeconomic differences in dietary quality. Dietary imbalances were more pronounced among rural residents, males, low-educated individuals, and low-income groups. Imbalances among urban residents, males, and high-income individuals were primarily driven by “excess”, while those among rural residents, females, and low-income individuals stemmed mainly from “insufficiency”. Conclusion Although dietary quality among Guangdong adults has improved over the past two decades, it remains at a moderate level of dietary imbalance. Future efforts should establish a comprehensive intervention system tailored to urban and rural contexts through precise policy measures.