The cross-beam method has been used in calculations of load distribution, flow velocity, ultrasonic speed, and so on. This paper shows that the method is also mostly feasible to be utilized in optics-based measurement of suspended solids in liquid. We present a prototype of a measurement probe that has a set of two near-infrared emitter–receiver pairs and employs the cross-beam method. Our laboratory experiments, focused on measurements of H2O−SiO2 solid solution, show that the developed probe has good sensitivity and can linearly measure the concentration of suspended solids with a wide dynamic range. The presented prototype is suitable for a broad range of applications. In particular, we demonstrate its suitability for monitoring sedimentation in water.