Due to its advantages in estimating regional and temporal land surface variables, satellite remote sensing has great potential in detecting and monitoring land surface wetness. In this paper, the preliminary characteristics of LST-NDVI space were analyzed by using land surface temperature (LST) and normalized difference vegetation index (NDVI) obtained from the Earth Observation System/MODerate-resolution Imaging Spectroradiometer ( EOS/MODIS). The results indicated that when the study area was large enough, and the time series length of the datasets was long enough, the distribution of the points in the LST-NDVI space is not triangular or trapezoid shapes. Based on this fact, a method for estimating the values of the dry edge and wet edge was proposed, the values of dry edge and wet edge were the sets of maximum and minimum at the given NDVI internals, the NDVI and LST values on the dry edge and wet edge were not linear relationship. A land surface Temperature -Vegetation drought Difference Index (TVDI) was constructed based on the LST-NDVI space characteristics, its potential on land surface wetness assessment over the Loess Plateau was explored. The results showed that there was a relationship between the land surface wetness denoted by TVDI anomaly and meteorological drought cased by precipitation anomaly, both of them matched well at the spatial and temporal patterns. There was a good relationship between TVDI and 5. 0 cm depth soil moisture over the Loess Plateau mesa, the correlation coefficient was above 0. 67, it passed the test of significance at the significance level of 1 percent. Therefore, it could be concluded that TVDI is able to be used in assessing land surface wetness.