In this study, the guidelines approved in Decision No. 1460/QD-TCMT dated November 12th, 2019 of the Vietnam Environment Administration were applied to assess Dam Voi lake’s surface water quality belonging to Tran Yen district, Yen Bai province. To perform this process, the authors monitored and analyzed 13 indicators of surface water samples in April and May in 2021 at various three positions. The data shows that all 13 indicators of all samples are in the allowed limitation of B1 column in the National technical regulation on surface water quality QCVN 08–MT:2015/BTNMT, including pH, NO3-, Cl-, Cd, Pb, total iron (Fe), TSS, COD, BOD5, NH4+, NO2-, PO43- and coliform. It means the water of examined regions only consists of irrigation and other equivalent purposes. Moreover, calculated WQI values indicate that the water quality of Dam Voi lake was almost excellent, except for the end area of the lake (NM3 site). The WQI values show that the water quality of the NM3 site was at a moderate level, which is caused by the increase of Pb content. Importantly, these results could be a database for future researches in the monitoring process of water quality changes at Dam Voi lake.