The invention discloses a method and a system for online trading by a community commodity storeroom. According to the method and the system, a merchant delivers commodities to be sold to the community commodity storeroom arranged in a resident community, and commodity relevant information is upload to a merchant website and a community commodity storeroom computer network platform, and a user, the community commodity storeroom, an online management trading platform and the merchant are in network connection with one another through internet to perform interactive communication and form an online commodity trading system. The user logs in the community commodity storeroom computer network platform to select commodities, trading is performed by the online management trading platform, and a commodity pickup identification code of a selected commodity is obtained by the user; the user uses the commodity identification code to check the code and pick up the selected commodity in the community commodity storeroom, and after commodity pickup and quality acceptance, the user pays for the commodity to affirm on the online management trading platform; the online management trading platform performs cost transaction settlement with the merchant in real time or in period. The method and the system for online commodity trading by the community commodity storeroom are convenient, rapid, safe, reliable and extremely high in commercial value.