Abstract: In the era of big data， big data exerts a profound impact on public decision making， mainly gradual decisions， due to its characteristics of volume， variety， velocity and veracity. Big data makes it possible to access sufficient information， the relevance analysis of big data improves the pertinence of decision making， the dynamic analysis of big data contributes to the gradual improvement of decision making， and the analysis velocity of big data brings about timely decision making. Most importantly， the prediction ability of big data will improve the scientificity of decision making. However， big data prediction may make errors and leak privacies， so decision makers should treat objectively the prediction ability of big data and the government should strengthen data sharing and control and attach greater importance to the training of big data analysts.

Key words: big data, prediction, public decision making, mirroring society, scientific decision making