To reveal the influence of different depth-span ratio cross-section shapes on the structural mechanical response and surrounding rock pressure characteristics in hard rock highway tunnels, this paper conducts a systematic analysis of six depth-span ratio sections based on a typical deep-buried tunnel project using numerical simulation methods. Differences between traditional calculation methods, such as Protodyakonov's theory and the theory of highway tunnel design, and the numerical results are compared. Existing empirical formulas exhibit deviations under non-standard cross-sections and high in-situ stress conditions, failing to adequately reflect the cross-section shape effect. Addressing the limitations of the Q system model, a quantitative coupling relationship between the depth-span ratio and surrounding rock pressure is established, and a modified surrounding rock pressure model based on the Q-method is proposed. Results indicate that: As the depth-span ratio increases from 0.2 to 1.0, the crown settlement decreases by 87.4%, and the peak surrounding rock pressure drops by 57.6%. When the depth-span ratio exceeds 0.6, structural deformation tends to stabilize. The modified model shows good agreement with measured data, validating the rationality and engineering applicability of the proposed method. The research findings enhance the theory of shape effects in hard rock tunnels and provide a reliable basis for structural design and rapid estimation of surrounding rock pressure under complex geological conditions.