Mirror neurons are a class of sensorimotor neurons in the monkey premotor and parietal cortices. These neurons have both motor and visual properties: they discharge not only when a monkey performs a goal-directed action, but also when the monkey passively observes a same or similar action performed by another agent. Because the observed action seems to be “reflected”, like in a mirror, these neurons are called mirror neurons. Over the years, due to the restriction of research ethics, the techniques of single-cell electrodes-implanted can not be used in human brain research. Therefore, it was not certain that whether or not there are also mirror neurons in human brain. However, through the studies of brain image such as TMS, PET, EEG, MEG and FMRI, it is now certain that there are some brain areas which have same or similar functions as mirror neurons. These brain areas are called mirror neuron system. In this article, the significances of mirror neurons and human mirror neuron systems are discussed in depth. It states that: (1) Just because of the mirror mechanism that can match action observation with action execution, the observer’s neural network involved in action execution will be activated by just seeing others’ actions. Mirror neuron systems project the perceived actions back onto one’s own motor representation of similar actions, the individual will automatically and unconsciously perform a dynamic simulation of the observed action in one’s own motor system. This simulation, in turn, allows the individual to create directly an embodied understanding of the observed person’s thoughts, feelings and intention of behavior. (2) The fact that mirror neurons fire both in action execution and in action observation shows that The mind and body are not two kinds of substance, but an integrated one. Our body's physical and physiological processes and our mental processes, in the essence, are different respects of the same activity of adaptation. They are one activity instead of two. it seems that mirror neurons bridge the gap between mind and body. It opens a new vision for reconsidering the mind-body relationship and provide a strong neurophysiological support for the unity of mind and body. (3) Mirror neurons unify action perception and action execution, enable us not only to understand the intentions and actions of others, but to build social networks, allowing us to feel another’s emotions such as joys and pains as our own. By means of the shared neural underpinnings, others’ intention, feelings and emotions become our own. Thus, mirror neurons act as a “neural bridge” between different individuals in social communication.