This paper focus on studying the elastic of modified cement mortar by polyethylene (stress-strain) curve in order to have Young's elastic modulus, this made by tri-phases modeling that allow to determination the property of this item depending on the property of it's three components individual. The validation of the proposed model has been studied extensively depending on a sample of cement mortar divided into two groups, the first one patterning normal cement mortar, second patterning modified cement mortar by Polyethylene witch substitute five percentage ratio of weight of sand by the same ratio of Polyethylene. Modified cement mortar is treated as composite of three components, Sand, Paste cement and Polyethylene. It's will be proposed models involving series, parallel and series-parallel coupling. This composite action is described by series-parallel model in which a portion of paste acts in parallel with sand and polyethylene and the remaining portion in series with this parallel coupling. Then according to the model we get Young's elastic modulus theoretically, reliance basic modulus factors of components. The proposed model is calibrated and verified by means of data set by experiment modulus results perform on cast samples in laboratory. It was found quite agreement of measured modulus factors experimentally versus theoretically.