<p>The complex relationship between multiple design parameters and several crashworthiness indices introduces substantial complexities in the structural design of variable-thickness rolled blank (VRB) and orthogonal woven glass fiber-reinforced polymer (OW-GFRP) hybrid hat-shaped beams under transverse impacting. The complexity arises from two primary factors: the direct relationship between structural parameters and crashworthiness indices remains unclear; and the sensitivity of structural parameters to crashworthiness indices can vary markedly across different design schemes, leading to prolonged design cycles and elevated costs. Therefore, we introduce two intermediate field variables, internal energy density (<i>IED</i>) and its mean square error <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\delta _{IED}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>δ</mi> <mrow> <mi mathvariant="italic">IED</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>, to systematically quantify structural energy distribution patterns enabling the exploration of nonlinear relationship and the sensitivity analysis via spatially <i>IED</i> gradient. This approach constructs a unified framework for the optimization design of structural crashworthiness. The effects of structural parameters on crashworthiness indices, internal energy density and its mean square error are carried out by the numerical models validated by three-point bending experiments of hat-shaped beams. It is found that a more homogeneous <i>IED</i> distribution leads to better crashworthiness indices. Moreover, sensitivity analysis of design parameters to crashworthiness indices has been performed through the surrogate model constructed by the response surface method. The results indicate that the thickness of VRB thick zone (<i>t</i>) has the most pronounced effect on crashworthiness indices, with the number of OW-GFRP plies (<i>n</i>) also playing a significant role, while the influence of middle position of transition zone (<i>p</i>) and the ply angle of OW-GFRP plies (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\theta\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>θ</mi> </math></EquationSource> </InlineEquation>) is comparatively limited. Finally, a design criterion for homogenizing the <i>IED</i> distribution is proposed to inform the structural design of hybrid beam, which has been successfully applied to a VRB/OW-GFRP hybrid bumper, achieving both excellent crashworthiness and significant mass reduction.</p>