The long-tailed distribution characterizes many Internet traffic properties which are often modeled by Lognormal distribution, Weibull or Pareto distribution theoretically. However, it is rather difficult to directly apply these models in traffic analysis and performance evaluation studies due to their complex representations and theoretical properties. This paper proposes a Hyper-Erlang Model (Mixed Erlang distribution) for such longtailed network traffic approximation. It fits network traffic with long-tailed characteristic into a mixed Erlang distribution directly to facilitate our further analysis. Compared with the wellknown hyperexponential based method, the mixed Erlang model is more accurate in fitting the tail behavior and also computationally efficient. Further investigations on the M/G/1 queueing behavior also prove the efficiency of the Mixed Erlang based approximation.