A new concept of Approximate Non-diffracting Grating Structured Light (ANGSL) and its implementation method are proposed. ANGSL has characteristics of long focal-depth, narrow strip-width, steady light field, and constant light intensity in certain rang etc. An optics system with a precise triangular-section prism is set up to produce ANGSL.Applying Huygens-Fresnel principle and Kirchhoff theory, theory analysis and calculation are completed. The distribution of the light field is simulated in the non-diffracting range. Experimental results show that experimental data is in good agreement with the theory calculation. According to system parameters, ANGSL is produced with 18 μm strip-width and 570 cm non-diffracting range, whose strip-width and intensity distribution do not change with transmitting distance. Compared with traditional light source, ANGSL has advantages of high resolution and precision in the application of 3D profile measurement.