For an inertial-confinement-fusion cryogenic target, the fusion ice layer inside the capsule should have a uniformity more than 99% and an inner surface roughness less than 1 μm (root mean square) to avoid Rayleigh-Taylor instabilities. And this highly smooth ice layer required for ignition is generated in the presence of volumetric heat and affected by the thermal environment around the capsule. For the D ₂fuel targets, the uniformity of the fusion ice layer inside the capsule is consistent with the uniformity of the surface temperature around the capsule, and the latter can be controlled by directional infrared illumination. A major challenge of directional infrared illumination is the precision of directional infrared spatial distribution. In this paper, a numerical model coupling the directional infrared tracking and temperature field calculation is proposed and validated by experimental results. A three-dimensional physical model of the cryogenic target is used to study the influences of different forms of directional infrared spatial distribution errors on the temperature uniformity of the capsule. The results show that the eccentricity of IR band axis has the worst effect on the temperature uniformity of the capsule, followed by the distance between both IR bands, and the width of the IR band has the least effect on the temperature uniformity of the capsule. Therefore, the eccentricity of IR band axis should be avoided in experiment to ensure the uniformity of the temperature of the capsule, further ensuring the uniformity of the fuel ice layer inside the capsule.