Abstract: The important technical characteristics of PDS microdensitometer data acquisition system are the limiting qualification values of the instrument.In Ppractice the accuracies of density and coordinates rely on the linearity, noise,scan speed,scan direction,step length,apertureetc of the instrument and are confined to each other.aam relationship must be known before starting measurement in order to set higher data accuracy.Because the relationship between every PDS is different the technical parameters are variable and should be obtained from the instrument used and the image to be mezsured.In summary,the instrument should be used after its performances are clearly realized.The Precision PDS equipment in our laboratory has therefore been studied and analyzed, some significant results about the performances have been obtained.