The invention belongs to the technical field of 
infrared sensors, and discloses a wide-angle optical 
system for a passive-type 
infrared sensor. The 
system comprises an 
infrared sensor module group anda wide-angle lens group. The wide-angle lens group comprises a focusing 
lens array which is formed on the lens body and is used for gathering the infrared 
thermal radiation at each 
azimuth in a wideangle range; and a wide-angle 
concave surface or a wide-angle defocusing Fresnel surface which is formed on the lens body. The light gathered by the focusing 
lens array is refracted by the wide-angleconcave surface or the wide-angle defocusing Fresnel surface, and the 
view angle is reduced. After the reduction of the 
view angle, the gathered infrared 
thermal radiation is received by the infraredsensor module group. Through the setting of the focusing 
lens array which plays a role in focusing, the 
system achieves the gathering of the infrared 
thermal radiation at each 
azimuth in the wide angle range, and the gathered light is further refracted, and then the 
view angle is reduced. The light is received by the infrared sensor, thereby enabling the wide-angle detection function of the wholesystem. The overall structure of the system is easy to implement, and the system is small in size and is low in cost.