The paper analyses the measuring errors caused by frequency fluctuation of spectrum signal,puts forward a new integer-period sampling DPSD method,and discusses several noticeable points.At last the comparative signal-to-noise test results between this method and ALIA are presented.Theoretical analysis and test results show that signal-to-noise ratio was improved by more than one time compared to ALIA,this method can be used in NIR spectrometer's weak signal detection,and the spectrum signal can be acquired ...