An integrated design and optimization method of the microwave radiator used in a microwave chemical reactor is discussed.The radiator，made of high-borosilicate glass，is an important part of the reactor，by which the microwave energy is delivered from the microwave source to the cavity of the reactor.It is composed of radiating part，baffle and impedance matching part，to obtain better radiating effect.However，under the influence of the microwave energy，the thermal stress，resulted from the large variation of temperature when the reactor is working，may make the radiator crack，so that the reactor does not work properly，even leading to explosion.In order to avoid the above phenomenon，the design of reactor is modified.First，based on the analysis on the electromagnetic transmission characteristics of the radiator，in which the Maxwell equations are solved with the electromagnetic boundary condition by finite-element method，the structural parameters of the radiator is optimized，to make the reflection coefficient as low as possible to reduce the loss of microwave energy during the transmission.Secondly，the design of radiator is modified to improve its stability to avoid the excessive local thermal stress at the transition structure，in which the integrated analysis for multi-fields is applied by solving the Maxwell equations，the heat conduction equation and the thermoelastic equation.The desired results are obtained.The reflection coefficient is below -10 dB，as required，in the frequency range of 2.4—2.5 GHz，the thermal stress is reduced greatly from 17.62 MPa to 12.43 MPa，and the position with the highest thermal stress is away from the joint of the baffle and the radiating part，so that the radiator is more stable during the operation.This method can be applied to develop microwave radiators with good stability，and it is of practical value in the industrial production.