In magnetic confinement fusion (MCF), the plasma always exhibits an anisotropic temperature distribution, which may impact not only the plasma dynamics but also the nuclear reaction process. Here, through theoretical derivations and self-consistent particle-in-cell simulations with the newly-developed nuclear reaction and alpha particle energy deposition calculation modules, we find that, if considering the plasma has an anisotropic temperature distribution, the fusion energy gain factor ($Q$) of MCF is significantly modified, where both the deuteron-triton nuclear reactivity and the alpha particle energy deposition fraction are heavily influenced. The simulation results show that, under the International Thermonuclear Experimental Reactor (ITER) condition, if the plasma temperature anisotropy ratio can reach 0.1, i.e., the plasma perpendicular temperature component is one-tenth of its parallel component corresponding to the ambient magnetic field direction, the $Q$-value of ITER can be increased from the originally-designed 5 to about 10, with doubled enhancement.

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