The invention discloses a separation calculation method for strain measured by a cement-sand-gravel dam strainometer. Considering that compared with a common concrete, a cement-sand-gravel material is characterized by low elasticity modulus and high strain, the method calculates each strain component factor by a large deformation problem, and on the basis, a stepwise analysis method is used to separate each component of strain from strain measured by the strainometer step by step. The method is used for separation calculation for strain measured by a cement-sand-gravel dam strainometer. Aimed at the mechanical property of the cement-sand-gravel dam material, defects that component factor is based on small deformation hypothesis in concrete dam related calculation method is modified, and a strain separation method suitable for the cement-sand-gravel dam is obtained. The method has relatively high application value in aspects of cement-sand-gravel dam strain monitoring data analysis, dam body true strain dynamic variation rule research in construction and operation periods.