The present invention discloses a straight line fitting method. A coordinate system is redefined according to a traveling direction of a coal cutter, to help a user to visually observe a coal cutter track, and butt joint with a joint control coal cutter automatic memory cutting system is performed in real time, to perform linkage adjustment of a coal cutter running track and line motion control, horizontal control and height adjusting control of a working face, so that a problem that the coal cutter track is hard to analyze due to a geographic coordinate system is effectively eliminated. Therefore, high-precision inertial navigation positioning navigation can be performed on the coal cutter, real-time and high-precision data information such as speeds, accelerated speeds and displacementsin multiple directions of the coal cutter and precise data information such as a coal mining working face dip angle and a pitching mining angle are obtained, staff downsizing and efficiency improvement are effectively implemented, and a real sense of integrated joint mining machinery automation is accelerated. Coal cutter joint mining work efficiency and device reliability utilization are significantly improved, and intelligent coal mining production costs are reduced.