The inertial confinement fusion design requires smooth and uniform deuterium-tritium (D-T) ice layers in a spherical shell. One of the most important factors affecting the ice layer quality is the thermal environment around the capsule, which determines the low-mode thickness asymmetries of the D-T ice layer. In this paper, we report the thermal simulation results for the hohlraum cryogenic target in the China Academy of Engineering Physics, focusing on the ice layer roughness analysis and low-mode control. The simulations were carried out with a computational fluid dynamics code. A calculation procedure based on the dynamic mesh method was applied to predict the D-T ice layer profile. The sensitivity of ice layer low-mode roughness to some operating and thermal condition has been investigated. The conclusions in this paper provide better direction for our cryogenic target’s further design and improvement.