In order to minimize the total cost of distribution system and increase the vehicles' loading rate, the influence of simultaneous pickup-delivery on vehicles' loading rate is considered and a VRPSPD (vehicle routing problem with simultaneous pickup-delivery) model for urban express common distribution is established under the condition that express companies carry out joint distribution. Then an improved genetic algorithm is proposed to solve the model. Finally, the practicability and validity of the model and algorithm are tested by examples.