In order to assist the impact assessment and prediction in Environmental Impact Assessment framework, the Environmental Protection Administration (EPA) additionally provided ten technical guidelines. However, these announced guidelines did not cover all the issues and in particular, the guidelines designed for waterbody assessment has not addressed. Due to many development projects are unavoidably related to impact water quality in different ways, this study reviewed and collected the experiences from domestic and the U.S. implementations, and consulted the local experts, to establish the technical guideline draft of river water quality assessment. This guideline is aimed to improve the quality of EIA documents. The technical guideline draft included nine articles, one figures, and three annexes. The six assessment tools are suggested, i.e., mass balance, Streeter-Phelps equation, BASINS/HSPF, QUAL2K, SWMM, and WASP. The selection principles are based on the characteristics of projects and receiving waterbodies. One of the important model parameter is the designed flow and Q75 is suggested for those with efficient observation data; otherwise, supplemental sample in low-flow period is required. Wastewater flow should consist with the quantity of applied wastewater. The water quality impact in construction and operation period needs to be analyzed separately. In construction period, the Reduction Plan of Runoff Pollution is needed and the mass balance is used to assess water quality impacts from the reduced runoff wastewater. The proposed assessment tools in technical guidelines are particularly for impact analysis in operation period. Finally, ten realistic case provided by EPA document system are chosen to demonstrate the application of the technical guidelines. The results of the case studies with data from public information database, original EIA reports, and references ensured the feasibility of these models.