Unequal interval jump grey model was built for raw data series with unequal interval and jump trend in this paper. Levenberg-Marquardt arithmetic that belongs to non-linear least-square. estimation was used to recognize the parameters. The model built was used to fit spectrometric analysis values of diesel engine and the fitting precision is good. It is helpful to improve the accuracy and reliability of spectrometric analysis by revising test data after oil change with model parameter.