The current thermal efficiency of a diesel-hot-air stove in a greenhouse was low and NO_x emission was high. Based on the technology of exhaust gas recirculation (EGR), a new method for increasing thermal efficiency of a diesel-hot-air stove from a greenhouse was proposed. The unique EGR heat-exchange system of a diesel-hot-air stove of all-digital microprocessor-controlled intelligently was developed in a greenhouse. The system, which could give the optimized EGR characteristics needed by diesel-hot-air stove test was developed. The structure and principle of this EGR heat-exchange system were also introduced. This method as well as its validity was proved by the diesel-hot-air stove tests. The optimized range of the EGR rate all the way is from 50% to 70%, if the EGR rate is 60%, the thermal utilization efficiency of the EGR heat-exchange system of the stove was enhanced by 17.6 % as compared with no EGR rate. The pollution of the environment was reduced by EGR system. It is ideal that the EGR heat-exchange system of a diesel-hot-air stove substitutes for traditional heating system. The EGR system is suitable for diesel-hot-air stove.