Abstract: Based on the basic principle of the shape measurement by carrier modulation in electronic speckle pattern interferometry (ESPI) , a carrier pattern containing altitude information is formed on the object surface when the test object is tilted a small angle. The points on the surface of the object are displaced a distance when the test object is rotated. The phase difference introduced by the deformation and the phase difference introduced by the deflection of the object were compared. It is found that the carrier is introduced by the out-plane displacement and the phase containing altitude information is contributed by the in-plane displacement. Several ESPI methods for shape measurement by using carrier modulation are discussed. The typical ESPI system is effective in shape measurement because the carrier pattern containing altitude information is distinct and the phase of the object can be derived by Fourier transform easily.