A gas control system for a reflow soldering furnace, a furnace chamber of said reflow soldering furnace comprising a preheating zone and a cooling zone and containing a gas, said gas comprising oxygen and a working gas, a working environment of the furnace chamber requiring an oxygen concentration reaching a target set value (T V), wherein said gas control system comprises: an oxygen detecting device, said oxygen detecting device being capable, in use, of coming into contact with said gas in said furnace chamber, for detecting an oxygen concentration in said furnace chamber, wherein said oxygen detecting device generates an oxygen concentration signal based on the detected oxygen concentration, characterised in that the gas control system further comprises: at least one first intake valve device and second intake valve device, wherein said first intake valve device is configured, in use, to controllably establish fluid communication between the preheating zone and a working gas source, and said second intake valve device is configured to controllably establish fluid communication between the cooling zone and said working gas source, thereby inputting the working gas into said furnace chamber; and a controller, said controller being configured to control the opening extent of said one first intake valve device and second intake valve device based on said oxygen concentration signal, thereby regulating a flow rate of the working gas inputted into said furnace chamber, wherein the controller comprises a memory configured to store a regulation set value (R V) and the target set value (T V) of an oxygen concentration, said regulation set value (R V) being greater than the target set value (T V); and further characterised in that said controller is configured to: when an actual detection value (D V) reflected by said oxygen concentration signal is greater than said regulation set value (R V), increase the opening extent of said first intake valve device and that of said second intake valve device until said actual detection value (D V) is smaller than said regulation set value (R V); and when an actual detection value (D V) reflected by said oxygen concentration signal is smaller than said regulation set value (R V) and said actual detection value (D V) is greater than said target set value (T V), keep the opening extent of said first intake valve device at a preset value and decrease the opening extent of said second intake valve device until said actual detection value (D V) is equal to said target set value (T V). at least one first intake valve device and second intake valve device, wherein said first intake valve device is configured, in use, to controllably establish fluid communication between the preheating zone and a working gas source, and said second intake valve device is configured to controllably establish fluid communication between the cooling zone and said working gas source, thereby inputting the working gas into said furnace chamber; and a controller, said controller being configured to control the opening extent of said one first intake valve device and second intake valve device based on said oxygen concentration signal, thereby regulating a flow rate of the working gas inputted into said furnace chamber, wherein the controller comprises a memory configured to store a regulation set value (R V) and the target set value (T V) of an oxygen concentration, said regulation set value (R V) being greater than the target set value (T V); and further characterised in that said controller is configured to: when an actual detection value (D V) reflected by said oxygen concentration signal is greater than said regulation set value (R V), increase the opening extent of said first intake valve device and that of said second intake valve device until said actual detection value (D V) is smaller than said regulation set value (R V); and when an actual detection value (D V) reflected by said oxygen concentration signal is smaller than said regulation set value (R V) and said actual detection value (D V) is greater than said target set value (T V), keep the opening extent of said first intake valve device at a preset value and decrease the opening extent of said second intake valve device until said actual detection value (D V) is equal to said target set value (T V). when an actual detection value (D V) reflected by said oxygen concentration signal is greater than said regulation set value (R V), increase the opening extent of said first intake valve device and that of said second intake valve device until said actual detection value (D V) is smaller than said regulation set value (R V); and when an actual detection value (D V) reflected by said oxygen concentration signal is smaller than said regulation set value (R V) and said actual detection value (D V) is greater than said target set value (T V), keep the opening extent of said first intake valve device at a preset value and decrease the opening extent of said second intake valve device until said actual detection value (D V) is equal to said target set value (T V).