In order to explore the complex interaction mechanism of runoff and sediment transport, the sliding partial correlation coefficient was used to identify the variation points of water and sediment. The runoff and sediment series of the Tao River Basin were divided into two periods: 1956—2008 and 2009—2022. Based on the Copula function, the risk analysis of water and sediment encounters was conducted. The results showed that the sliding window values in the Taohe River Basin are different, and all reached the lowest point of the water-sediment correlation coefficient curve in 2008. The P-III distribution has a fitting degree of close to 1.0 for the runoff and sediment transport sequences in the Taohe River Basin during two time periods, indicating a good fitting effect. During two time periods, the joint distribution of water and sediment in the Taohe River Basin indicates that when both runoff and sediment transport take small or large values simultaneously, the correlation is relatively high. Among the three Archimedean-type Copula functions, the Euclidean distance of the Frank-Copula function is the smallest at 0.02, and it has the best fitting effect. During two time periods, the synchronous probability of water and sediment in the Taohe River Basin is 85.94% and 79.61% respectively, while the asynchronous probability is 14.06% and 20.39% respectively. The synchronous probability of water and sediment is significantly higher than the asynchronous probability. After the variation of the water-sediment relationship, the probability of synchronous water-sediment decreases, the probability of asynchronous water-sediment increases, and the correlation of the water-sediment relationship declines. The combinations of abundant water and abundant sediment, scarce water and abundant sediment, and moderate water and abundant sediment have a higher probability. The combinations of moderate water and moderate sediment, and scarce water and scarce sediment have a much lower probability. When the runoff and sediment transport in the Taohe River Basin are both abundant, the correlation is the strongest. The next strongest correlation is the combination of scarce runoff and abundant sediment transport, and the combination of moderate runoff and abundant sediment transport. The research results provide a basis for the prevention and control of water and sediment disasters and water and sediment regulation in the Taohe River Basin.