Precision diamond turning based on a fast tool servo (FTS) as a micro-displacement module is a very popular micro-structured surface manufacturing technology. The surface accuracy is a sticking factor that demands the need for a long-standing solution to fabricate ultra-precise freeform surfaces accurately and efficiently. This paper presents a surface characterization method for sinusoidal grid surfaces fabricated by FTS. The method includes data acquisition, data processing and pattern analysis. A series of cutting and measurement experiments have been conducted on sinusoidal grid surfaces using a two-axis ultra-precision machining system equipped with Fast Tool Servo and examined by a non-contact micro-surface profile system. The microscope images are analyzed by the two-dimensional discrete Fourier transform technique, which perfectly matches the nature of sinusoidal waves. A comparison studies on surface quality of machined surface based on constant-angle and constant arc-length methods have also been conducted.