Abstract: Density is one of key indexes for detecting and controlling the quality of compacted soil.Sand replacement method and water replacement method are used to test the density of compacted soil in the field of roadbed construction in our country at present. However, because of the shortcomings of inefficient detection for sand replacement method and low precision for water replacement method, it is necessary to develop a method with faster detection speed and higher precision,and then rubber balloon volumemeter has been developed to meet the demand. The structure,principle, sensitivity and test method of rubber balloon volumemeter are introduced. Detection precision of the instrument is assessed by comparisons between the tests with balloon method, sand replacement method and water replacement method in lab and itsitu, and with analytical method of random factor. The instrument is light,simple,and convenient to be operated with high precision.