The hydrological characteristics of Dongjiang River have changed greatly since 1980s. In order to study the characteristics of river channel under changing environment, the water level discharge curve of the main hydrological stations has been extended (referred to as “H-Q” curve) based on the K value analysis method, and the river roughness data at different flow rates are deduced using one dimensional mathematical model. The results showed that: The H-Q curve of Heyuan and ridge lower traffic stations changed little. The down-cutting of river bed at downstream of Dongjiang River lead to decrease of the H-Q curve at Boluo Station. Based on the historical K value, a relatively reasonable H-Q curve with high flow rate can be obtained. The roughness of Heyuan to Boluo section reaches 0.025-0.038. Some sections such as the Boluo-Jiantan section and the upper-lower corner have larger roughness (>0.03), which is related to the relatively large bed slope.