The problem of poor drainage system did not get due attention in most urban city of Ethiopia. In Assosa town flooding and surface water inundation are a common problem at time of rainy season. The primary objective of urban drainage system is to remove, control and guide the excess surface water to the right of way, that generated from different sources with least nuisance, danger, damage to people and the environment. The general objective of the study was to identify main cause of flood and surface water drainage conditions of the study area with recommendation of possible remedial solution to problems. In this study an exploratory and descriptive research methods were used to describe and explore the existing condition of drainage system. Primary and secondary data was collected, analyzed and presented using Microsoft-excel, Easy fit, Arc-GIs, graph and percentages. Landsat imaginary of 2005 and 2019 year for land use land cover classification was used. GIs software was used to classify the land use land cover map based on ground truth observation and accuracy assessment was performed to check the reality with ground truth. The result of Lulc was significantly shifts from one class to other. Frequency analysis of rainfall was computed using Gumbel and log Pearson type III method and the consistence of the data were checked by using GOF. IDF curve was developed to know the relationship between rainfall intensity, rainfall duration, and return period, whereas the peak discharge flowing in main catchment up to final outlet point was calculated by using rational method. To check the adequacy of existed drainage system, field investigation and measurement was taken at required point. The finding of the study indicated that the major causes of flooding were surface runoff flow is not guided to draining structures due to poor design, construction, inadequate connection between minor and major drainage line, lack of community awareness, shortage of disposal area, flood occurrences on street, blockage of drainage channels by solid waste and lack of operation maintenance for the drainage system. However, Arab sefer, Awura Godana area, Tena sefer, Bus station area and Arbe Gebeya sefer are a place that are highly vulnerable to surface flooding among the study area. Therefore, well designed and constructed drainage facility, maintenance of drains before the rain season, awareness creation for community and construction of additional new drainage system with sufficient dimension for the whole area of the town will help in the solving problem.