Abstract: The definition of volumetric joint count (JV) for rock mass is introduced firstly and the indexes of joint set spacing or frequency are more suitable to the definition of JV. The formula ' s suitability of volumetric joint count (JV) for rock mass is discussed and the study result indicates that this formula is only suit for rock mass with one through joint set or two to three perpendicularly through joint sets. And the result with this formula is usually bigger. After volumetric and joint persistence ratio modified, the formula of JV for rock mass is more suitable to rock mass with persistent or intermittent joint sets. With the modified JV, the degree of integrality for engineering rock mass is described objectively.