In order to study the spatial mechanical characteristics of concrete curved box girder bridge, taking an urban interchange ramp bridge with 9.75 m main beam width and 5 × 18.76 m bridge length as the engineering background, ANSYS finite element model is used to calculate several bridge models with standard span. The internal force ratios of different regions of the section are obtained by integral calculation of the section stress. The internal force ratio coefficient, stress difference and stress ratio are used as evaluation indexes to discuss the differences of bending moment, shear force and stress of each control section between curved box girder bridge and linear box girder bridge under one-stage dead load. It is found that under the first-stage dead load, the normal normal stress distribution of the top and bottom plates of the curved box girder is uneven, and the maximum shear lag coefficient can reach 1.35 ; the maximum shear force of the lateral web is 2.65 times that of the medial web ; When the center angle exceeds 8°, the shear ratio coefficient of the middle section of the side span is greater than 1.1, and when the center angle exceeds 13°, the shear ratio coefficient of the side span fulcrum section is greater than 1.13. Under the action of constant load, the neutral axis of curved box girder bridge is inclined, and the positive stress unloading occurs outside the middle section of side span, and the stress unloading occurs inside the section of side span fulcrum. The calculation results of beam finite element method commonly used currently cannot truly reflect the spatial stress distribution of curved box girder. The stress distribution of each web of box girder and the bending normal stress distribution of roof and floor should be paid enough attention to in engineering design.