How to acquire soil physico-chemical parameters instantly in the field is an important orientation of the research of soil science, and the technology is also a potential way to complement or replace the conventional soil laboratory analysis with field-based measurements. In 2008, a Working Group on Proximal Soil Sensing was formed in the International Union of Soil Sciences (IUSS). The working group is oriented to provide a platform for academic exchange on theories, technology, equipment and application of various proximal soil sensors. In this paper, researches on proximal soil sensors are classified per operation principles of the sensors and elaborated separately, and in the end, main problems and trends of the development of PSS are pointed out.