Abstract: In this article, The effect of fuel assembly deformation on the quadrant power tilt (QPT) was simulated using a studying object of VVER of Tianwan Nuclear Power Station (TNPS). By varying pitch values between fuel rods, fuel assembly deformation was simulated accordingly and thus its impact on QPT was investigated quantitatively. The simulation results show that moderation effect and nuclide effect are key contributors to the unbalanced fuel reactivity causing QPT indirectly.