Influence of capsule support tent on ICF DD gas implosion performance is investigated with a two-dimensional radiation diffusion hydrodynamic code LARED-S. It shows that the support tent reduces significantly the neutron yield with a YOC (yield over clean) of 55.2%. The main degradation mechanism is that the capsule shell produces high-amplitude high-density spikes, penetrating deep into the central DD gas. It increases greatly power loss due to electron conduction on the CH/DD interface, leading to the rapid reduction of DD reaction rate and final neutron yield. Compared with one-dimensional ideal implosion simulation result, bang-time of the two-dimensional tent simulation is apparently earlier, and perturbations introduced by the capsule support tent reduce the central pressure and internal energy of DD gas, which is converted from the shell implosion kinetic energy.