Cone parts are widely used in advanced manufacturing and precision mechanics, providing air proof, torque transmission and so on. The straightness of generatrix is one of the important parameters, and the required accuracy can be up to submicrometers. In order to realize the rapid and high precision generatrix measurement of smooth surface cone, a laser interferometric method is proposed based on the structure of typical Fizeau interferometer. The high precision optical flat is used for reference standard, and the surface of cone is the measured object. Two cylindrical lenses with different focal lengths realize unidirectional expansion of parallel beam, solving the problem of CCD camera fringe resolution. The interference fringes are curved because of the cone angle, and the peak is the basis for accurate determination of the generatrix. Two fringe processing techniques are described in detail, which are single-frame and phase-shifting methods. Single-frame method includes two steps, i.e. the calculation of integral part and decimal part. The advantage of this method is the simple measurement structure. Phase-shifting method needs piezoelectric transducer (PZT) to generate several steps for phase calculation, with the advantage of high accuracy. The experimental results show that the straightness measurement accuracy can be better than 0.2 μm.