Weirs are the most extensively used hydraulic structures in the different fields of hydraulics, environmental, irrigation, and chemical engineering, as flow measuring and flow control devices in open Channels. The object of the present paper is to study the effect of the geometry of crump weir on the coefficient of discharge (Cd) under different flow conditions. The experimental work was conducted in rectangular laboratory flume; fifteen physical models were used with five upstream angles (17o, 22o, 27o, 32o and 37o) and three different crest heights (10, 15 and 20) cm under free flow conditions. The results show that Cd value will increase with the decrease of crest height as well as with increasing flow rate; it is also directly proportional to the upstream slope and inversely to the downstream slope. Computational fluid dynamic (FLOW 3D) were used to conduct new experiments.An empirical relation was obtained to estimate the coefficient of discharge Cd under different height and upstream slopes crump weirs.