The laser metal deposition process is accompanied by the interaction of the forming environment and molten pool, which influences the solidification conditions and formed microstructure to a certain extent. To achieve the rapid production of large, complex, and high-performance metal structures, high-deposition-rate laser metal deposition (HDR-LMD, deposition rate ≥1 kg/h) technology was developed by simultaneously improving the energy and mass inputs based on the conventional laser metal deposition (C-LMD, deposition rate ≤0.3 kg/h) technology. Compared with the C-LMD process, HDR-LMD can change the shape and temperature of the molten pool, further influencing the forming environmental effect on the molten pool. Moreover, as the dimension of the forming part increases, the cost of establishing an environment chamber also increases. Based on the aforementioned background, the forming environmental effect (air and argon environments) on the solidification condition, single-layer geometry, and microstructure of HDR-LMD GH4169 superalloy was studied. Results show that although the heat dissipation of different environments influence solidification condition during the HDR-LMD process, their influences on the oxidation are very small. Moreover, compared with argon environment, air environment exhibits a greater cooling rate, finer primary dendrite arm spacing, less Laves phase content, and lower degree of microsegregation. This study indicates that the solidification condition and microstructure of HDR-LMD GH4169 alloy does not significantly improve upon being shielded with argon, which can provide a reference for industrial production.