Generation and generation gap are two ancient concepts but revive in the transition of digital society. This paper argues that generation involves biological, social and family attributes and medium is the key factor triggering generation gap. With the popularity of digital media, the old generation gap combines with the new digital divide to evolve into digital generation gap. We conceptualize and operationalize digital generation gap at three levels (i.e., macro/national, meso/ social and micro/family) and three dimensions (i.e., access, use, and literacy). Based on data from a national survey of 948 families with 3282 respondents, we conducted basic analyses and comparisons of the micro/family and meso/social level of digital generation gap and discussed the way of calculating Digital Generation Gap Index (DGGI) at the macro level.