An accurate cutting length calculation method for space-warped closure segment which considers the erection deviation of closure port was proposed. To obtain the optimization model drived by the internal penalty function method and calculate the ridge line cutting length of closure segment accurately, an objective function with distance between the characteristic points of closure port and the ridge lines of closure segment was constructed, and the constraints of the erection deviation of the closure segment were satisfied. The closure time was determined by the correlation analysis of the temperature field and deformation with 72 h measured data. The temperature influence correction method of the cutting length was proposed based on weather forecast and the correlation analysis on temperature field and ambient temperature. The steel pylon closure with zero additional stress and high precise came into fact due to closure segment cutting calculation method based on the coordinates of multi-feature points.