To scientifically implement conservation actions (ten-year fishing ban) on fish biodiversity in the Yangtze River, it is necessary to understand the dynamic changes in fish resources. Through a combination of literature review and field surveys, this study conducted a quantitative analysis of the changes in body length of representative Yangtze River fish since the 1980s and explored the indicative role of these changes in resource recovery. The research results showed that: 1) analysis of body length changes in seven typical fish species in the Yichang River section over the past 10 to 40 years revealed these changes are closely related to biological characteristics; high resource base values, wide-ranging feeding habits, low age of sexual maturity, and strong fecundity were associated with greater increase in body length after the fishing ban; 2) analysis of the body length of fish communities in the four waters of the Yichang reach, Jinsha River, Chishui River, and Dongting Lake over the past 20 to 40 years shows that changes can be roughly divided into three stages: decline, fluctuating increase, and obvious increase. This corresponds well with the progress of the fishing ban. 3) The average body length of Coreius heterodon and dominant fish communities in the Yichang River section is positively correlated with the catch per unit fishing effort (correlation coefficients are 0.66 and 0.88 respectively), indicating that the fish body length is closely related to resource abundance. 4) The analysis and prediction of the body length of the fish community in the Yichang River section based on the logistic curve showed that the value would reach 1.22 by 2030, which is close to the characteristic value in the 1980s. This suggests that fish resources in the river section can be restored to the resource levels of the 1980s by 2030. This study found that changes in fish body length in natural waters are closely related to the health status of populations and communities and have a positive effect on resource abundance and changes. The body length of fish can be used as an important reference indicator for routine monitoring of fish resources in the Yangtze River.