Considering the regulating capacity of DC power transmission system to power and voltage， a new model of dynamic reactive power optimization of AC/DC system is proposed. The objective of the model is to minimize all-day network loss of the AC/DC system. Various constraints are taken into account， including power-flow constraints， DC variables constraints in control equations， dynamic constraints of discrete control variables， and security constraints of voltages. It is a multi-period nonlinear mixed integer program problem. Based on the hybrid algorithm， a hybrid intelligent algorithm for dynamic reactive power optimization of AC/DC system is proposed. Test results of modified PSASP 36-bus system demonstrate the efficiency of the proposed model and algorithm， and show that dynamic reactive power optimization has potential in the loss reduction of an AC/DC power transmission grid.