With advantages of simple framework and compact dimension, Seeker based on polar pointer with slick chain is one of the key components of modern miniaturization precision guide weapons. For polar axis and slick chain, its object-to-imager coordinate conversion is more complex compared with traditional seeker. Clear and accurate object-to-imager coordinate conversion is necessary for seeker tracking moving objects when guiding attack. The object-to-imager coordinate conversion expression was reasoned out by quaternion application in coordinate conversions. The conversion was proved by modelling and simulating in Matlab.