PURPOSE: Carbon dioxide supply controlling system and method applying the environmental weight are provided to prevent the environmental contamination by preventing the oversupply of carbon dioxide gas. CONSTITUTION: A carbon dioxide supply controlling system comprises the following: first and second CO2 sensors(11, 12) detecting the CO2 amount of two divided spaces, separately; a solar sensor(13) detecting the quantity of sun light; an indoor temperature sensor(14) detecting the indoor temperature; a humidity sensor(16) detecting the humidity; a data setting unit(17) setting the feeding time of CO2, the standard CO2 value, the standard range for the solar radiation value, the solar radiation limit value, and the humidity limitation and ventilation window opening extent; a data saving unit(24) saving data values from the data setting unit; a controller(18) controlling the gas supply from a CO2 feeder when the detected humidity is higher than the standard value; a monitor display unit(19) displaying images by
