The logistic scheduling is a typical combinatorial optimization problem. Vehicle routing optimization is one of the most critical parts in logistics, and the Vehicle Routing Problem (VRP) is an important problem occurring in many distribution systems. This paper proposes an improved ant colony optimization algorithm to optimize the dynamic assignment to the Capacitated Vehicle Routing Problem (CVRP) and the Vehicle Routing Problem with Time Windows (VRPTW). The improved algorithm tests several different combinations and derives the solution that is able to deliver more orders at the correct delivery date. Results show the effectiveness of the proposed algorithm.