We re-examined the interplate coupling in terms of backslip rate at the Nankai-Suruga trough beneath the Tokai region with a 3-dimensional GPS time series and a refined plate boundary model. We reanalyzed the GPS data and reconstructed plate boundary configuration. Then we inverted GPS velocities to infer the interplate coupling during April 1997 to April 2000. Our results show that a maximum back slip rate of 2 cm/yr was found at the depth of 15--25 km around 137.42E, 34.32N. We also estimated interplate coupling for the period from January 2001 to December 2002. This time period coincides with a slow slip event found by Ozawa et al. <2002>. Forward slip up to 3 cm/yr was inferred beneath western region of Lake Hamana. And, we found that the epicenters of low frequency tremors are located there, suggestive of a close connection between the occurrences of the slow slip event (SSE) and low frequency tremors.