This paper addresses the correlation dimension of R-R intervals under Heart Rate Variability (HRV) conditions according to chaos theory. We calculate the R-R interval dimensions of normal people\'s waking and sleeping status, and of different status of a 24-hour clinical Holter recording. The results show that the bigger the HRV is, the smaller the dimension of R-R interval is. This method needs small data and costs little time to calculate, so probably it can be of clinical use in the analysis of HRV.