Continuous measurement of flow for a channel section is usually impractical or very expensive. However, stage can be observed continuously or at regular short time intervals with comparative ease and economy. In the paper, we measured the stage by ultrasonic finder and calculating discharge from velocity measured by current meter and channel size. According to the discharge and stage of the cross-section, we fitted the rating curve and further made the hypothesis test to verify the real relationship between stage and flow. This will help the local authority to decide the amount of water diverted from the reservoir to farmland and improve the irrigation efficiency.