Abstract: A multi-object optimization mathematical model with strict constraints has been developed for the heat recovery system in the first stage conversion furnace of large-scale synthetic ammonia plants (1000 t/day). Optimal synthesis was conducted through graphic solutions combined with optimizing calculations, employing the optimization theory for large complex system in system engineering Comparing with the original design, it was found that significant increases in heat recovery efficiency can be obtained with the new design scheme. Additional capital investment is not called for to adopt the new schema, neither would there be any increase in operating cost to achieve similar energy recovery as in the original design.