Focusing on the evaluation requirements of IR Imaging Air-to-Air Missile′s adaptability to complex environment,the concept and compositions of complex environment are established and discussed.The complex environment means the composition of different kinds of things and their interacting factors which are difficult to be analyzed and understood by the IR seeker.Factor complexity and countermeasure complexity are defined to describe the complex environment.The seeker′s index system is established,and the correlation between complex environment′s indexes and seeker′s performance indexes is also researched.Furthermore,the evaluation rules including Probability Rule and Efficiency Rule are given.Simulation scheme and evaluation index system are also proposed.One simulation and evaluation platform for IR Imaging Air-to-Air Missile including typical target and decoy module,background module,missile module and simulation evaluation module is established.This platform realizes fast and accurate adaptability evaluation and provides basis to improve the design of IR imaging seeker.