The airborne electro-optical platform system is usually used to identify the sensitive or fixed target, which can provide laser irradiation designation for semi-active laser guided weapon. In order to evaluate the irradiation accuracy of the laser designator that integrated with electro-optical platform system, theoretical analysis and numerical simulation are performed for the irradiation accuracy, which is changed with atmospheric turbulence intensity and laser propagation distance, and the field tests about irradiation error is carried out that caused by parallelism of optical axis based on actual equipments, the irradiation errors measured in the three tests are about 0.352 5 mrad、0.521 9 mrad and 0.511 3 mrad, respectively. The results show that the designation error would be increased as designation range and atmospheric turbulence intensity increase, and the designation error induced by parallelism of optical axis is about milliradian magnitude, which effectiveness is much larger than the atmospheric turbulence.