Storm water drainage system in urban areas became a deterministic system, especially in light of the current climate changes. This system eliminates the excess water resulting from heavy rainfall, which leads to disruption of daily life. Irregular maintenance of the network system, problems appear, especially the blockage of the covers or network pipes, which affects the efficiency of the network. This study deals with the experimental investigation of blockage on storm network system and the relationship between efficiency of the system and blockage parameters. Many scenarios of blockage within grate and pipe were studied and its impact on storm system efficiency calculated. For the pipe system, two scenarios were studied; the first one is the blockage of end main pipe with relative blockage height (15%, 30%, 50%, 70%, and 90%). The second one is the blockage through the main pipe with relative blockage height (25%, 50%) and relative blockage length (33%, 67%, and 100%). For grate, the blockage is investigated with the blockage area ratio (12.5%, 25%, 37.5%, and 50%). In addition, the combined blockage of grate and pipe was studied. Finally, an equation has been created to estimate the system efficiency as a function of blockage ratios and system discharges. The results indicated that for surface blockage (12.5%, 25%, 37.5%, and 50%), the discharge efficiency decreased as the amount of blockage increased with different grate blockage by (17.8%, 19.3%, 21%, and 24.6%), respectively