The rapid development of outsourcing logistics provides new contract design issues, and it is important to study the delivery time contract design under different task structures. From the fourth party logistics perspective, delivery time contract design of outsourcing logistics is considered, and the principal-agent models are established to aim at the serial and parallel task structure respectively. The methods for determining the optimal contract are given, and the results of the optimal contract are analyzed. Finally, numerical experiments verify the effectiveness of the delivery time contract design method under two different task structures.