Most IEEE 802.11 DCF analysis models concentrate solely on the performance of homogeneous traffic sources (i.e., with the same arrival rate), only a small number of literatures focus on heterogeneous mixed service networks (i.e., saturated or nonsaturated). In current research, the network nonsaturated and backoff freezing analyses are not accurate. This study proposes a new and improved bi-dimensional Markov chain model to analyze the performance of the DCF mechanism under heterogeneous traffic sources with the M/G/1 queuing model. Moreover, it extends the existing models to take into account previously-ignored MAC layer factors such as backoff freezing and limited times of retry. By solving the steady-state of this model, it allows the calculation of the three important parameters:per-station and network throughput, mean delay, and transmission packet loss. Through the relevant theoretical simulation and analysis, it is proved that the model can well analyze the performance of the DCF mechanism, taking into account the actual application scenarios, thus can analyze the performance of the DCF mechanism better than others under heterogeneous traffic sources.