In order to take into account both the investment and reliability in transmission expansion planning， a mathematical model for the short term integrated expansion planning of real and reactive power for transmission network considering static security risk is formulated. The sum of the lines cost， reactive power compensation， operation cost and risk cost are considered as an objective function. The probability of contingency and AC power flow constraint are included in the model. For the purpose of achieving static security risk assessment based on the AC model， a two-stage approach for load curtailment based on active power steady-state security region and voltage sensitivity iteration is proposed. Firstly， the amount of load curtailment is determined by implementing optimal remedial control measures. Secondly， the risk cost could be measured by the social production value of the load loss. To cope with the computing complexity when solving the model presented， a two-step optimization algorithm is provided， through which not only is the difficulty of the problem significantly reduced， but also some satisfactory solutions can be identified to support planners in decision-making. The simulation results obtained for SBS 46-bus system demonstrate the soundness of the model and the effectiveness of the algorithm.