Gallium Nitride(GaN)-based materials have the characteristics of large band gap, high electron mobility, high thermal conductivity, etc., which are used in various electronic devices and optoelectronic devices, and have received extensive attention. High power GaN-based blue laser diodes (LDs) have great prospects in laser display, laser lighting, metal processing and other fields. However, the development of high-power GaN-based blue lasers is extremely difficult, mainly related to the difficulties of epitaxial growth, processing and packaging technology. Firstly, the epitaxial structure of blue laser is complicated, and the crystal quality needs to be ensured while improving the luminous efficiency of the quantum well and reducing the light absorption loss. Secondly, the sidewall loss and cavity surface loss need to be reduced during the manufacturing process. Last but not least, a low thermal resistance packaging technology needs to be developed, so that high-power GaN-based blue lasers can effectively dissipate heat. In this work, by adopting the double-sided packaging method for GaN-based blue lasers, which use the copper fully attached to the N-side of the blue laser to increase the heat dissipation. According to the change in the forward voltage caused by the junction temperature change, the thermal resistance of the single-sided packaged blue laser is 8.5 K/W, while the double-sided packaged blue laser has a thermal resistance of 6.7 K/W. It can be found that the GaN-based blue laser with double-sided packaging has lower thermal resistance and can dissipate heat more effectively, which is beneficial for the high-power blue laser to work under continuous room temperature conditions. According to the power-current curves of the blue laser from room temperature to 65 ℃, the characteristic temperature of the single-sided packaged blue laser is 132 K, and the characteristic temperature of the double-sided packaged blue laser is 235 K, it is found that the characteristic temperature of the double-sided packaged blue laser is higher, which means that has better temperature stability. Finally, we demonstrate the double-sided packaged blue lasers with a ridge width of 45 μm and a cavity length of 1 200 μm which have a threshold current density of 1.1 kA/cm² and a slope efficiency of 1.4 W/A. The light output power reaches 7.5 W at 6 A under continuous-wave operation at room temperature, it means that the double-sided packaged blue laser has good material quality, structure and packaging.