Martadireja 1 street Section is one of the roads in the city of Purwokerto which still often experiences inundation due to drainage channels that cannot accommodate or drain surface water. Based on these problems, it is necessary to identify the causes of the Martadireja 1 street channel that is not functioning optimally. Rain that occurred on February 18, 2019, resulted in a pool caused by heavy rains at that time. This study aims to analyze the drainage capacity of Martadireja 1 road using the Rational method. The data used is rainfall data from Arca station. Based on the hydraulic analysis the results of the study show that the existing drainage capacity is still able to accommodate rainwater runoff because the Q existing canal (0.595 m3 / sec) is greater than the Q planned canal (0.021 m3 / sec). The existence of now day's puddles is caused by the daily volume of rains is more than the pass 10 years, which happen to be 82 mm/hour.