In this paper, a novel straightness/coaxiality measurement system using transversal Zeeman dual frequency laser is introduced. In contrast to longitudinal Zeeman system, the size of instrument is shortened and the non linearity error generated from quarter wave plate is avoided. The system is self adaptive and quite resistant to air turbulence. Phase measurement can reach 0.1 degree equivalent to 1 μm. Measuring component can be removed from light path during measuring process. Using 8098 singlechip computer to stabilize the beat frequency intelligently, experiment has shown that the change of beat frequency is less than 0.5 kHz in 10 hours. The measuring stability is about 2 μm/h. Correlation coefficient of linearity of indicating value is better than 0 9999. It realizes the straightness/coaxiality measurement of long range.