In the process of silage production, the compactness and moisture content will affect the quality of silage and even lead to failure of silage. But most instruments are designed to obtain a specified parameter which is unable to accurately evaluate the silage quality. A combined probe was designed to simultaneously measure the compactness and water content of silage based on the American Society of Agricultural and Biological Engineers (ASABE) standard. Cone angle was 30°, probe diameter was 12.83mm and probe length was 50mm. According to the principle of resistance strain and frequency domain method, the moisture electrode and resistance strain gauge were designed in the cone probe. In order to evaluate the applicability of the combined probe, calibration and validation were carried out with a motoroperated penetrometer. The calibration included two processes: power stroke and return stroke. The force calibration test showed that, in each process, there was a linear equation with a determination coefficient (R2) of 0.99 relating the output of the combined probe to force values within the range of 0~1kN. The water content calibration was tested by ten kinds of silage samples, and it was showed that the water content was linearly related to the outputs of the combined probe in the range from 29.9% to 67.8%, and the determination coefficient reached 0.909. The validation was tested by three kinds of silage samples, and it was demonstrated that the combined probe could response the variation of the compactness and water content of silage simultaneously and eliminate the effect of penetration friction component.