Abstract: The tactical missile seeker handover accuracy from midcourse to terminal guidance is researched.The small perturbation method is proposed to analyse error sensitivity of the seeker presetting parameters from error sources.Firstly,the terminal guidance seeker presetting parameters are computed,based on the equations of a surfacetoair missile movement and a target movement.Then the seeker presetting unaccuracy due to the command guidance radar measurement errors is also computed.It can be seen that the seeker presetting errors increase rapidly when the missile is close to the target,which leads to an important conclusion that the late seeker handover from midcourse to teminal guidance should be avoided.