Leakage through the panel gaps of the dish leads to gain loss and noise temperature increment. For the radio telescope antenna, which peruses ultra-high sensitivity, this effect cannot be ignored. This paper investigates the leakage and resulting noise temperature variance of the Square Kilometre Array(SKA) dish sub-reflector, in conjugated with the structure design and manufacture procedure of the panels. By electromagnetic analysis, the effect of the leakage due to various panel designs is evaluated, and the structure design of the sub-reflector panel is decided, fulfilling the requirement of SKA.