Abstract: In present plant and animal complementary ecosystem, the ratio of plant growing area to animal raising area varies greatly that causes CO₂ concentration too high or too low, and the effect of CO₂ enrichment is reduced. Under the condition that a CO₂ transfering installation is equiped and the CO₂ distrbution along the greenhouse is even, a mathematic equilibrium model of CO₂ transfer is established and a computer program for dynamic simulation of CO₂ concentration is developed and verified. Based on the appropriate greenhouse CO₂ concentration and taking a tomato and fattening pig complementary ecosystem in Shenyang district as an example, the suitable proportion of tomato growing area to the number of fattening pigs is calculated, which supply a basis for the construction and administration of the ecosystem.