Combining the 10 kV distribution system structure and operational feature, a voltage and reactive power optimization model incorporating no-load variable transformer in distribution systems is proposed. According to the tap ratios of off-load tap changer transformer can be adjusted in special time, the actual load are equal to multi-stage dynamic load. This model can provide the optimal tap ratios of transformers adapting the whole segment, optimal capacitance and running voltage in several segments. Genetic algorithm is adopted to solve voltage and reactive power optimization model with the least net loss as objective function. It is introduced main procedure of genetic algorithm and improved method, which is efficient and practical by the computations of 10 kV distribution system.