Molecular reconstruction is an effective tool to predict the detailed composition of complex mixtures under obtainable bulk properties and chemical details. With the introduction of statistical distribution, although the number of variables in the model is reduced, the ranges of statistical distribution parameters have a great influence on the prediction accuracy. A novel parameter estimation method using the analysis of the probability density plot of gamma distribution based on the basic available information is proposed to obtain parameter ranges with wide universality and non-specificity. The obtained ranges are used in a molecular reconstruction model to predict the bulk properties and molecular composition of naphtha. The model assumes molecular composition within each homologous series follows a gamma distribution against carbon number. The results of a naphtha sample show that the calculated bulk properties and molecular composition are in good agreement with the experimental values.