High speed ball-screw system has serious friction heat to form thermal expansion to each component. An analyzing model considering with contact deformation and thermal expansion is established in realizing positioning error for a high speed ball-screw system. A finite element model of nut is also built in calculating elongation of nut. Surface strain of nut is measured by strain gages in order to confirm with data obtained from finite element model. Temperature of nut and screw were also measured by thermal couples and are used in calculation of elongation by the use of linear elongation equation. The tendency of positioning error is well estimated by the analyzing model. The model can be used in feedback positioning control factor and develop precision high speed ball-screw system.