Abstract: Objective To address the problem of fitting a straight line in three-dimensional space,since the equa-tion is a six parameter equation,not a simple linear relationship,the traditional least squares methodcannot be used to solve it.In this paper,a new method of space line based on the total least squares isproposed.Firstly,the number of parameters was decreased from six to four by changing the standardequation of the straight line,then re-expressed the equation in the form of a matrix.Therefore,thefitting problem was transformed to the parameter-solving problem in total least squares.Further,thefitting four parameters were obtained using a TLS iteration,and the six parameters of the space lineswere recovered through a backtracking method.An experiment in the paper verifies the effectivenessand applicability of the new method.