Main goal of the paper was to investigate the wasting of the Atlas cedar (Cedrus atlantica (Endl.) Manetti ex Carrière) in the national park of Théniet El Had (west of Algeria).We have installed 59 temporary plots of circular shape and a surface of 10 acres each to study this effect. At the level of each plot, we have performed measurements (density, basal area, dominant circumference and dominant height), analyze of soil (pH, organic matter, humidity, rate of limestone, texture and nitrogen content) and noted some site parameters (exposure, altitude, slope and micro relief). The results show that the total basal area and density of trees are very important in the plots of the altitudinal floor 1400-1600 m, oriented toward the north and steep slope (>20°) where there is a positive relations on soils basaltic and texture of sandy-loam soils. The soil has an average depth at low varies from one canton to another. It is sandy-loam type with a pH of 5.92 to 7.8, not salty rich in organic matter, poor in nitrogen and non-limestone. The decline of the Atlas cedar is frequent through the northeastern, sunniest and driest exposures, along the altitudinal range between 1400 and 1600 m, where water losses are greater than the contributions on slopes > 20°.