In recent years, container technologies have attracted intensive attention due to the features of light-weight and easy-portability. The performance isolation between containers is becoming a significant challenge, especially in terms of network throughput and disk I/O. In traditional VM environments, the performance isolation is often calculated based on performance loss ratio. In container environments, the performance loss of well-behaved containers may be incurred not only by misbehaving containers but also by container orchestration and management. Therefore, the measurement models that only take performance loss into consideration will be not accurate enough. In this paper, we proposed a novel performance isolation measurement model that combines the performance loss and resource shrinkage of containers. Experimental results validate the effectiveness of our proposed model. Our results highlight the performance isolation between containers is different with the issue in VM environments.