Precision guided weapons are the most important operation objects in regional electronic air defence combat, and especially the electrooptical guided weapons using infrared, television or laser guidance hold absolutely large proportion. Jamming target assignment, whose accuracy and rationality determine the jamming efficiency and own target safety, is a key point in the combat. The target character, own electronic warfare capability and decision difficulties are analyzed to establish the basic processing route of jamming target assignment, and the solution is based on multilayer defense. Then as the basis of target assignment, threat assessment of the jamming target is researched, and an assessment method based on knowledge reasoning is proposed to adapt to uncertain target environment. Finally, based on the target threat assessment results, the jamming target assignment model is built for different targets, countermeasures, and deployment of jamming resources, which is aiming at maximal jamming effectiveness index. The simulation result shows that this method can positively respond to target situation changes, and it has timely assignment, precise jamming and adjustment capacity to satisfy the actual combat requirement.