Hydrogen desorption properties of Li-N-H system (composed of LiH + LiNH2) doped with LiBH4 as catalyst and microwave absorber have been investigated under microwave irradiation. The results showed that pure Li-N-H system can not be heated effectively by microwave irradiation, but it can be rapidly heated up to 500 degrees C within 5 min with 7.6 wt.% LiBH4 addition by a microwave heating with a power of 400 W. Further study indicates that it is Li4BN3H10 generated during the ball milling process that acts as the microwave absorber and catalyst. Li-N-H +7.6 wt% LiBH4 by microwave heating desorbed 4.95 wt.% hydrogen which is 3.6 times more than that of Li-N-H +7.6 wt.% graphite by electric resistance heating at 250 degrees C within 30 min, indicating that the desorption kinetics of Li-N-H system is improved by the combination of the catalytic effect of Li4BN3H10 and microwave irradiation. Furthermore, the isothermal kinetics of Li-N-H with 7.6 wt.% LiBH4 under microwave irradiation were well fitted by Johnson-Mehl-Avrami-Kolmogorov (JMAK) model and the activation energy was 43.9 kJ/mol H-2 which is significantly lower than that under electric resistance heating, demonstrating that the desorption kinetics of Li-N-H with LiBH4 addition could be effectively improved by microwave irradiation.