Abstract: Thunder defence and grounding system is indispensable part to mobile radars or fixed radars. Because the power voltage that the digital circuit and analogue circuit use is lower and lower, the anti-jamming and protection grade of the system is higher and higher, the design of the grounding and thunder defence system is becoming a more and more important part in modern radar design and the important basis to ensure the safe and reliable operation of radars. This paper gives an overall analysis on the design of the grounding and thunder defence system and analyzes in engineering the methods of the system design.