In view of the present measurement of soil compactness based on the cone index, eliminating the influence of soil friction on compactness measuring is impossible.It needs to ensure sensor is inserted into the soil at constant speed, thus it is difficult to use and the accuracy is not high. In order to improve the real-time measurement precision and maneuverability of soil compactness, a real-time soil compactness detection sensor was designed based on the cone index, and the synchronous measurement of acceleration was realized, which eliminated the error caused by different speed in the process of the metal rod inserting into soil, as well as improved soil compactness measuring precision. Homemade sensor had good static characteristics and dynamic characteristics through a large number of test. Measuring range was 0~7800kPa, sensibility was 0.041896, the stability of the standard deviation was 5kPa, measuring accuracy was ±0.02%FS, overshoot was 7.81%, and transient time was 0.632s. Compared with SC-900 soil compactness meter of the United States, its accuracy of the linear fitting coefficient of decision reached more than 0.96. The results showed that the homemade soil compactness sensor and SC-900 soil compactness meter had consistency of performance in the actual measurement, and homemade soil compactness sensor was more convenient and cheaper.