Robotics technology brings innovation for agriculture industry. In order to solve the grain issue and the labor force issue in the world, the smart agriculture is an important approach at present and in the future. In this paper, a new path planning method based on wind direction is proposed for agricultural unmanned boat which is susceptible to the effect of wind. This method could be utilized in an arbitrary convex quadrilateral paddy field or a pond where the agricultural robot boat could navigate automatically. The simulation and field test shows that when the boat does farm work, the new path planning algorithm could cover the whole farm field under the minimum effect of wind.