Abstract: In order to gain a deeper understanding of the changing law of water-sand relationship in the Jialing River, based on the annual runoff and sediment load data of Beibei Hydrological Station at the outlet of the Jialing River from 1965 to 2022, the Mann-Kendall test, double cumulative curve method and the physical genesis method were used to diagnose the variation points of water and sediment relationship, and the marginal distribution function and Copula function of the runoff and sediment load were preferred through the AIC, BIC, and RMSE, and the optimal Copula function was determined, and the water-sediment joint distribution model of the Jialing River basin was established. The established model was then used to calculate the probability of water and sediment abundance and depletion encounter, joint and co-occurring recurrence periods in the basin, and then to compare and analyse the univariate and joint variables design values of water and sediment. The results show that:（1） The water and sediment relationship changed abruptly in 1989, and the water and sediment correlation before the change was stronger than that after the change.（2） The optimal marginal distributions of the water and sediment series in 1965-1989 are Logn, and the optimal joint distribution model of water and sediment is the Gumbel Copula model, while the optimal marginal distributions of runoff and sediment in 1990-2022 are Gamma and GP respectively, and the optimal joint distribution model of water and sediment is the Frank Copula model.（3） The synchronous probability of the two stages of water and sediment sequences is 59.77% and 61.14% respectively, both of which are greater than the asynchronous probability, and the probability of occurrence of the extreme cases of “abundant water and sediment depletion” and “depleted water and sediment abundance” is extremely low, which indicates that there is a large correlation between the probability of water and sediment, and the water and sediment conditions are relatively stable.（4） The design value of the joint variable is larger than the univariate one, and the design value of runoff and sediment load calculated by the joint distribution of the two variables is more reliable. The joint recurrence period of water and sediment is concentrated near 2 years, and the majority of the co-occurrence recurrence period is less than 50 years. By exploring the characteristics of the joint change of water and sand in the Jialing River basin, this study can provide a reference for water and sand regulation, disaster prevention and mitigation in the basin.