This study focused on the residual stresses (RS) generated by laser beam on a DP600 steel. During laser welding, the parts are locally heated by an intense laser beam followed by melting and solidification. The RS in the ferritic phase of a 2.5 mm thick plate have been experimentally determined with neutrons and laboratory X-ray diffraction techniques and numerically using Abaqus software. This study is aimed at characterizing the residual stresses (RS) distribution of a Dual Phase steel (DP600) undergoing laser beam welding with two different laser parameters. We used a laser beam, Nd:YAG, composed of the 4 kW generator with an arm robot type Fanuc R2000iB for welding operation. The diameter of the optical wire is 200 µm with a laser focus spot diameter of 560 µm and a focal length of 583.5 mm which corresponds to the focal point reference on the surface. Argon is used as a shielding gas with a flow rate of 20 CFH (Cubic Feet per Hour) on both surfaces of the blanks. To evaluate the properties of the welded joint such as the residual stresses, we welded by transparent mode two steel plates of both 1.25 mm thickness. The welding was conducted at a speed of 3.4 m/min and a power of 3.5 kW in full penetration mode with thickness of 2.5 mm for the overlapping area with a lap joint gap of 0.1 mm. Residual stresses were determined non-destructively by neutrons diffraction measurements carried out on the dedicated 2 axis DIANE diffractometer at Laboratory Léon Brillouin (LLB). Experimentally, we realized the measurements on the upper face of the weld bead in longitudinal, transversal and normal directions with different laser parameters. The results show clearly the influence of the laser parameters. The residual stresses evolution is the same in two samples but the values, in particular the maximum, are different in the two samples. The results confirm that the laser welding lead to a mechanical gradient both transversally on the surface and we can control the residual stresses with the laser parameters. The temperature near the FZ and HAZ rapidly changes as the distance increases from the heat source. The variation of residual stresses follows the thermal cycle of laser process and so the laser parameters. The comparison between, experimental and numerical results showed the same trends considering the residual stresses in the ferrite and the studied zones. For each butt welding parameter studied, similar curves were obtained. There is a relatively good correlation between experiments and numerical results: the FZ is in tensile with values in the order of 450 MPa. The study in the transversal direction gives the same distribution: BM and HAZ with low values (about 50 MPa). In the longitudinal direction of the welding, the simulation results do not show differences and give us values around 450-500 MPa.