Based on the aluminum alloy components in the space propulsion system， the characteristics of threshold of laser welding are studied. Results show that the threshold interval of laser welding for aluminum alloy is positively correlated with the welding speed and the absolute value of defocus， but the magnitude of the positive change is much lower than that of stainless steel， nickel alloy and titanium alloy. For laser welders with different beam qualities， the smaller the focal spot diameter of the beam， the lower the threshold interval during real-focus welding； the smaller the divergence angle of the beam， the lower the threshold interval under the same defocus amount. In the range of -12° to 12°， the threshold interval of laser welding for aluminum alloy has nothing to do with the incident angle. The blowing direction and blowing speed of shielding gas basically do not change the threshold interval of laser welding for aluminum alloy， which is different from stainless steel.