The invention discloses a field image acquisition device, which comprises a base with a cavity and a camera, and is characterized in that the base and the camera are placed at an interval, a main stage is installed on the base, at least one pair of measuring claws is movably arranged between longitudinal edges of the main stage of the main stage, the longitudinal edges of the main stage are provided with graduations matched with the measuring claws; the main stage is provided with a plurality of water channels extending into the cavity of the base, and a background baffle plate is installed at a transverse edge of the main stage; a clamping device is arranged at the surface of each water channel; each clamping device comprises a fixed piece fixed at one side of the surface of the water channel, and the fixed piece is internally provided with a push rod; and one end of the push rod is connected to an arc-shaped baffle plate located at the edge of the water channel, and the other extends out of the fixed piece. The measuring method comprises the steps of firstly, installing a field image acquisition device; secondly, taking pictures; thirdly, importing the pictures into a computer, and acquiring a transform expression; fourthly, calculating the actual length of a blade; and fifthly, calculating the actual width of the blade. According to the invention, the rice can be enabled to be keep the natural growth state in the measuring process, and accurate values of each parameter of the blade can be acquired simply and quickly.