5min。Based on virtual instrument and bionic olfaction technology, the sampling method, sampling time and sample weight of silver carp stored at 4℃ were investigated by our home-made electronic nose with four gas sensor array during storage; PCA (principal component analysis) method was employed to optimize experiment parameters. The result indicated that the improved free air diffused method was the optimal sampling method, which can simplify the sample equipment compared to the traditional headspace method. The optimal measurement conditions for evaluating freshness of freshwater fish are 60gfor sample weight, free air diffused method for sampling method and 5min for sampling time.