This paper presents a numerical model to simulate the behavior of the slender RC column strengthened by a steel jacket using angles and strips. The proposed strengthening technique has been verified using experimental results of slender column tests performed by previous research. Both load-deformation relationships and failure modes are investigated. The results of the numerical models are in good agreement with the values from the experimental work used in verification. The results also show that the strengthening technique using steel angles and strips is effective for increasing the ultimate load of the slender column by up to 50% and also increases column stiffness and ductility. It’s found that the capacity of the strengthened column increases with steel angles and strips sizes and decreases with increasing slenderness ratio (λ)