In this paper, we study the state-dependent symmetric Gaussian interference channel, where the additive Gaussian state is non-causally known at both transmitters but unknown to either of the receivers. We apply the coding scheme in [5] with different dirty paper coding parameters. We study both strong and weak interference scenarios and characterize the theoretical gap between the achievable symmetric rate and the upper bound, which is shown to be less than 1/4 bit for the strong interference case and less than 3/4 bit for the weak interference case. Finally, we provide numerical evaluations of the achievable rates against the upper bound, which validates the theoretical analysis for both cases.