The invention discloses an in-field tray placement method. The workload of manual growing tray placement is large, and the working environment in a field makes people feel fatigued more easily. A trayplacement device adopted in the method includes a ridge power guide rail, a ridge auxiliary guide rail, a longitudinal moving device and a tray placement trolley. The longitudinal moving device includes a Hall sensor, a moving guide rail, a connecting frame, a support frame, a first deceleration motor, a second deceleration motor, an intermediate wheel and a side wheel set. The tray placement trolley includes a frame, an axle, a longitudinal moving drive part, a position adjustment mechanism, a tray clamping jaw mechanism, a lifting mechanism and wheels. The position adjustment mechanism includes an adjustment block, a hand wheel, a screw rod and a handle. The tray clamping jaw mechanism includes a tray placement drive component, a tray placement frame and a clamping jaw component. A camis used for driving a tray clamping jaw, a stack of growing trays can be gradually placed one by one through the reciprocating motion of the tray clamping jaw, the structure is compact, and movement is reliable.