This paper investigates an UAV-assisted secure communication problem, in which, amidst the presence of unauthorized user, an UAV is designated to deliver information to the authorized users. The objective is to achieve the maximum the average confidentiality-rate through the joint optimization of transmit power and flight path. In particular, the transmit power constraints and the UAV continuous dynamic constraints are imposed. Experiment results are provided to illustrate the advantages of the planned trajectory in this paper compared with that of existing work.