The properties of warm dense matter are crucial for understanding the physics underlying star formation, stellar evolution and inertial confinement fusion (ICF). We present soft X-ray measurements of a well-isolated warm dense plasma system produced by the collision of high-speed plasma jets in ICF-related experiments with double-cone targets. The colliding plasma was found to exhibit a structure consisting of a hotter inner core and a colder outer shell. The core region emits continuum Planckian radiation with an effective temperature of $45.53\pm 0.44\;\mathrm{eV}$. The outer shell, which has electron density of around ${10}^{23}\;{\mathrm{cm}}^{\hbox{--} 3}$ and temperature of $34.26\pm 2.12\;\mathrm{eV}$, introduces absorption lines of carbon ions superposed on the continuum spectra. Two-dimensional radiation hydrodynamic simulations and synthetic X-ray spectral images reveal the detailed physical processes determined with the experimental measurements.