As the development of CMPs,the size of a onchip cache increases and it consumes more and more power of the whole system. How to reduce the power of cache has become a focus of many designers of modern caches. This paper investigates a lowpoweroriented runtime mechanism for shared cache partitioning. A shared cache partitioning framework is proposed,and it uses the Miss Rate Monitors to collect the miss rate information of the current applications at runtime. Then the miss rates are inputted to a lowpoweroriented cache partitioning model to get the partitioning solution within the performance degradation threshold (PDT). Our evaluation,on top of a two core CMP processor with a shared L2 cache,with 21 multiprogram workloads,shows that when PDT is 1% and 3%,the rates of L2 cache shutdown will be up to nearly 20.8% and 36.9% respectively.