The improved GPS (Geometrical Product Specification) system uses uncertainty as an economic tool to enable optimum allocation of resource amongst specification, manufacturing and verification. For a given GPS standard-chain, the key question is to calculate the compliance uncertainty. The determination of compliance uncertainty is a complex question because specification uncertainty and measurement uncertainty arise from many causes and propagate through the GPS standard-chain. A calculation method for compliance uncertainty of GPS standard-chain is proposed in this article. According to ISO 17450-2, a GPS process should be either in default state or special state. The biggest difference between the two states is that whether the specification operator is accordant with the verification operator. Aiming at the two states, the flow for the computation of compliance uncertainty is given respectively, and a case study is applied in default state. Results show it enables to generate compliance uncertainty on the verification of a GPS standard-chain, which makes the acceptance or refusal of GPS characteristic can be conducted in a quantitative way, so the veracity of verification could be improved.