The joint space or frequency are more suitable for the definition of volumetric joint count Jv in the Code of Engineering Rock Mass Classification. The suitability of Jv for rock mass with one, two or three sets of persistent joints is discussed. A correction factor K1 of Jv is calculated with the formula: K1=|sin(n1,n2[DD(-1][HT5SS]^[HT][DD)])||cos(n1n2,n3[DD(-1][HT5SS]^[HT][DD)])| . The influence of intersection angles between different joint sets on Jv is discussed. Then the definition of Jv for rock mass containing intermittent joints is deduced on the basis of joint persistence ratio with a new formula of Jv=K1[DD(]i[DD)]Sini(i3). The degree of joints in rock mass could be expressed more objectively with the proposed formula.