The ultrasonic surface wave is an important method to detect the quality of laser cladding layer. In order to improve the detection resolution, the phased array surface wave which can achieve the focusing effect of acoustic beam is used to detect laser cladding layer. Firstly the finite element model of surface wave propagation between single probe and phased array is established. Subsequently, the ultrasonic wave propagation path is studied based on the Fermat principle and the delay characteristics of the array elements. The focusing and deflection of the phased array surface wave are realized, and the influence of the thickness of the cladding layer on the focusing characteristics of the phased array surface wave is studied. The results show that when the base material is aluminum and the cladding layer material is 45# steel, the thickness of the cladding layer is within 2.5 mm, and the energy of the focal point decreases with the increase of thickness. Especially, the energy of the focal point decreases by 58.8% with the thickness of 1 mm compared to 0.2 mm. When the thickness is greater than 2 mm, the energy changes little at the focus point, indicating that the ultrasonic phased array surface wave has a good detection effect on the thin cladding layer.