Recent years have witnessed our major progresses in understanding the membrane-bound receptors on NK cells. Although functional studies of ligands for these NK cell receptors provide good opportunities to study roles of NK cells in anti-tumor and anti-virus immunosurveillance, little was known about how these ligands expression were modulated under physiological and pathological conditions. Several recognition models have been proposed to explain such an issue, which include "missing-self", "induced-self" and "modified-self" recognition model. Here stimulatory immunoreceptor mediated NK cell activation will be reviewed, and possible recognition mechanism by which NK cells operate during interaction with target cells will be discussed in details. Tumor escape from NK cell-mediated immunosurveillance will also be further addressed.