You can use different perspectives to classify sensors: their conversion principle ( sensor the basic physical or chemical effect); their use; their output signal type and the production of their materials and technology. According to the working principle of the sensor, the sensor can be divided into physical and chemical sensor two categories: sensor working principle classification of the physical sensor application is the physical effects, such as the piezoelectric effect, the phenomenon of magnetostrictive, ionization, polarization, thermoelectric, photoelectric, magnetoelectric effect. The measured signal of small changes are converted into electrical signals. Chemical sensors including those by chemical adsorption, electrochemical reaction phenomenon for the causality of sensor, the measured signal is small changes will also be converted to electrical signals. Some sensors can be divided into physical class, also cannot be divided into chemical class. The majority of sensor is based on physical principles operation. Chemical sensor technology problems, such as reliability, the scale of production possibilities, price problem, to solve this kind of problem, chemical sensor applications will have tremendous growth.