With the rapid development of renewable energy power generation， its intermittence and stochastic of output power have significant influence on available transfer capability（ATC）. The characteristics of the renewable energy power generation， e.g. the intermittence， stochastic， load fluctuation， and status uncertainty， are simulated through Monte Carlo simulation method. The ATC under specific status and parameters of system are solved through optimal power flow. The probability density of ATC samples is defined by applying probability statistics theory to establish a risk benefit model， and to achieve ATC with maximum comprehensive benefits. To analyze the influence of renewable energy power generation on ATC， with respect to position of power generation equipment， uncertainty of power output and penetration level etc. The method is validated by simulation on a modified IEEE 118 system involving wind power and solar power.