A Monte Carlo approach is appplied to the error estimation and error analysis of X-ray diffraction standardless quantitative phase analysis and the coefficient of its variation is cal dilated .which is compared with the error estimation by the condition number of the coefficient matrix of linear equations. The Monte Carlo error estimation is applied to the standardless quantitative matrix-flushing method, in which the mixture of KC1. CaCO3. ZnO and BaCO3 is analyzed as an example.