The structures of biomacromolecules are conventionally characterized by crystallography and cryogenic electron microscopy . The requirements of sample preparation limit the understanding of the specimens in their native states. Small-angle x-ray scattering (SAXS) has the capability of obtaining structural information from biological specimens in solution. However, resolving the structure from the acquired one-dimensional (1D) diffraction data requires the prior knowledge of the sample, and no unique solution can be guaranteed. Coherent diffraction imaging (CDI) provides excellent uniqueness in 2D/3D phase retrieval while the resolution is restricted by the poor signal-to-noise ratio at high-angle scattering. Here we combine CDI and SAXS to directly image a 19-nm-sized nodavirus particle in solution and determine the core-shell density distribution at a 1.3 nm pixel resolution. With 77,170 diffraction patterns summarized from randomly distributed nodavirus particles, the structural information can be obtained from the diffraction intensity alone without preknowledge. The hollow density distribution of a nodavirus particle revealed by our reconstruction is consistent with the structural determinations from crystallography and cryogenic electron microscopy. We believe this work represents a new protocol for characterizing the structures of macromolecules in solution from accumulated x-ray scattering data.