A ″sandwich″ structure based on copper-diamond is proposed, the thermal stress and Smile of the proposed structure and traditional Cu+CuW hard-solder packaged laser are studied by finite element analysis. Comparison of simulation results shows that the thermal stress of the new package structure is reduced by 43.8% and the Smile value is increased by 95%. When the coefficients of thermal expansion of laser chip and submount are matched, the submount materials with larger elastic modulus can better buffer the thermal stress of the chip. Taking the widely used Cu+CuW hard-solder package structure as an example, the influence of negative electrode and substrate thickness on the Smile of diode laser chip is studied. It shows that when the thickness of the negative electrode increases from 50 μm to 300 μm, the junction temperature of the chip decreases by 2.26 ℃, the Smile value decreases by 0.027 μm, and the thermal stress increases by 22.95 MPa.When the thickness ratio of the substrate to the heat sink is less than 29%, the Smile value increases with the increase of the thickness of the heat sink, and when the ratio exceeds the critical point, the Smile value start to decrease. Hard-solder packaged semiconductor lasers have a maximum Smile value of 3.876μm at a critical thickness of 2300 μm. Hard-solder packaged 976 nm lasers with CuW thicknesses of 300 μm and 400 μm are fabricated. The luminescence spectra are measured. By comparing the peak wavelength shifts, it is found that when the CuW thickness increased by 100 μm, the red shift of wavelength increased by 1.25 nm. According to the effect of temperature and stress on the wavelength, the stress is reduced by 18.05 MPa; the average Smile values of the devices are also measured, which are 0.904 μm and 1.292 μm respectively. Experiments show that the increase in CuW thickness can reduce the stress in the chip, but increase the Smile value.