<p>The construction and operation of the Pinglu Canal, a new land-sea corridor in Southwest China, are impacted by the incoming suspended sediment from its tributary. This paper reports a field study on the water–sediment processes of Xinping River, a main sediment-producing tributary of the Pinglu Canal. In-situ monitoring of discharge and suspended sediment transport rate was performed for 6 months at a cross-section near the confluence of Xinping River. The obtained data were used to investigate the characteristics of flow and sediment transport of the tributary. The results indicate that both the daily discharge and sediment transport rate at the monitoring cross-section exhibit significant seasonal variations. The wet period is the primary time for water and sediment transport from Xinping River into the Pinglu Canal. The clockwise loop is the main suspended sediment concentration and discharge (SSC–<i>Q</i>) hysteresis pattern in Xinping River, indicating that sediment near the confluence may be frequently transported into the canal. Sediment rating curve expressing the SSC–<i>Q</i> relationship suggests that the Xinping River Basin is less eroded and sediment-supply limited. However, larger discharges are expected to transport massive sediment from the channel to the canal annually. From this view, a relationship between discharge and sediment transport rate with a high correlation coefficient and an acceptable error is proposed to estimate the suspended sediment transport rate in Xinping River, aiding the design of sediment control measures at the confluence.</p>