  The source of the Galactic Lithium (Li) has long been a puzzle. With the
discovery of Li in novae, extensive research has been conducted. However, there
still exists a significant disparity between the observed abundance of lithium
in novae and the existing theoretical predictions. Using the Modules for
Experiments in Stellar Astrophysics (MESA), we simulate the evolution of nova
with element diffusion and appropriately increased the amount of 3^He in the
mixtures. Element diffusion enhances the transport efficiency between the
nuclear reaction zone and the convective region on the surface of the white
dwarf during nova eruptions, which results in more 7^Be to be transmitted to
the white dwarf surface and ultimately ejected. Compared to the previous
predictions, the abundance of 7^Be in novae simulated in our model
significantly increases. And the result is able to explain almost all observed
novae. Using the method of population synthesis, we calculate Li yield in the
Galaxy. We find that the Galactic occurrence rate of nova is about 130 yr^{-1},
and about 110M Li produced by nova eruption is ejected into the interstellar
medium (ISM). About 73\% of Li in the Galactic ISM originates from novae, and
approximately 15\%-20\% of the entire Galaxy. It means that novae are the
important source of Li in the Galactic.
