The water evaporation is a basic process occurring during the service life of cementitious materials. In this paper, the evaporation process of water from heated cement specimens with different composites were studied by low field nuclear magnetic resonance. The results show that there is a linear relationship between the signals intensity and water filling index. The non-evaporable water in the specimen contributes little to signal intensity. In addition, the relaxation signals have selective sensitivity. It could be used as a non-destructive method to the quantitative research of physically bound water in the cementitious materials.