It is well known that the low-coherent light source being used in interferometer permits to register the zero path difference with comparably wide range of measurement definition. This property is often used to determine the surface displacements by corresponding moving of the reference mirror and measuring its position. The conditions of measurement definition become more complex when the object being inspected has a non-smooth surface and there are many surface points which to zero path-difference condition are satisfied in different referent mirror positions. Such conditions were analyzed statistically by means of calculation of intensity cross-correlation functions of interference patterns performed in initial and consequent non-smooth surface positions. The tolerant range of the meanings of angular spectrum frequency deviations and lateral displacements of rough surface was determined by computer simulations. Different spectral characteristics and coherence lengths of interferometer illumination were verified and capacity of researched method was confirmed.