It is difficult to measure a complex object with a deep hole quickly by traditional three-dimensional (3D) profilometry, such as phase measurement profilometry or Fourier transform profilometry. A new 3D profilometry based on fringe modulation ratio is presented and a coaxial measurement system is designed. It is proved that the fringe modulation ration instead of phase can be used to determine the height distribution of the object because the height of a point of the object is proportional to the log value of modulation ratio of the point. A look-up table of height and modulation ratio is established through system calibration. To obtain the height map of the object, a sinusoidal grating pattern is projected onto the surface of a testing object. Two fringe images of the object are captured by CCD at two different positions. Modulation ratio is computed by Fourier analysis and the height of the point can be obtained by look-up table. The proposed 3D measurement technique can perform 3D shape measurement fast without suffering shading problem. The relative error of the measurement of a step with 79.51 mm height is 0.86%. Experimental results demonstrate that the proposed scheme can be useful for 3D shape measurement.