For reckoning geometric shape of existing spatial where different node position deviations have correlation, SSS (spatial system sampling) methods and statistical inference methods based on SSS are proposed. In a comprehensive consideration of the research on spatial structure node position deviation and the space sampling theory， the sampling mode and the minimumsamplesize formula are given for onsite detection of existing spatial structures. Based on the node position deviation correlation coefficient matrix and the hypothesis testing theory of nonindependent samples under normal population, a priori accuracy semiprobabilistic model of the existing structure is established by statistical inference. For a singlelayer 5ring K6 reticulated shell test model, a variety of numerical modeling methods are used to establish the calculation model for conducting comparative analysis of the overall stability ultimate bearing capacity, which verifies that the numerical model based on the spatial system sampling method is closer to the actual structure.