The invention relates to a method and a system for playing network multimedia data. The method comprises the steps of download playing and memory management. In the step of download playing, multimedia data from a download source is received and cached in a blocked mode, and the multimedia data is played; and in the step of memory management, timing monitoring or a deletion operation is carried out on the cached data amount according to a playing position when the data amount of cached multimedia data of a sub-block reaches a predetermined reference amount. The beneficial effects of the invention are that monitoring or deletion is carried out on the cached data amount while the multimedia data is downloaded and played, and a phenomenon of equipment blocking caused by too high memory occupation because of excessive caching is avoided. In addition, problems of repeated download and bandwidth waste possibly caused by a mode of deleting as soon as being watched through monitoring the data amount.