Serious soil erosion can endanger human survival and sustainable development. Therefore, simple and highly efficient soil stabilizers that can be used to treat loess soil, which has poor water stability and easily disintegrates, are a topic of concern for researchers. In this work, a biomass-based polymeric soil stabilizer (CXZ) was prepared using a “green” strategy with polymerization of carboxymethyl cellulose and xanthan gum. A direct shear test, unconfined compressive strength properties, water stability, and erosion resistance were systematically investigated to test the stabilization performance. The stabilizer agglomerated small loess particles into large aggregates through “coating” and “weaving” effects to increase the cohesion, water stability, and erosion resistance significantly, as demonstrated by Fourier transform infrared spectroscopy and scanning electron microscope. Furthermore, in a 30-day growth experiment, the number of alfalfa plants and the plant height in stabilized loess both increased with the increase in CXZ stabilizer concentration. This work provides insight into a novel biomass-based soil-curing agent, broadening its applications in loess remediation and soil erosion control.