Abstract: In this paper ,The new adjustment model of three-dimensional coordinate transformation-SARC (Step-by-step Adjustment with Restricted Condition-SARC) is presented. There are three main terms in this paper: (① regarding) the original coordinates(the aim coordinates) as observation with errors or true values; ② determining original value of the transformation parameters and linearizing observation equations accurately; ③ calculating the most probable values and variance of the transformation parameters by SARC model.