Abstract: In order to solve the problem that it is difficult to obtain sub-micron machining accuracy using traditional macro-interpolation algorithms in electrochemical micromachining, a variable-parameter sampling interpolation algorithm for constant-precision control is proposed. The data sampling increment is controlled in real time and the tool path is optimized by online measurement of the machining axial deviation. The precision control coefficient is introduced to realize constant precision control of parametric curve machining. The machining axial deviation and shape error of the algorithm are simulated by MATLAB. When the precision control coefficient k=1, the shape error is about 0.69 times of the pulse equivalent. The microstructure electromachining experiment was carried out using the algorithm and the sub-micron machining accuracy was obtained. The algorithm solves the machine tool motion online according to the machining state without pre-stored code, which can meet the high-precision machining requirements of special micromachining technology.