Abstract: An air-suction maize precision metering device has been early developed in recent years. It is very necessary to balance the seeding position and transverse movement of seeds for better seeding uniformity at high speed. In this study, a systematic investigation was made to clarify the influence of speed and seed distance on the seed drop uniformity in the maize precision metering device with air suction under high-speed conditions, particularly from the mechanical point of view. At the same time, a mathematical model of adjacent seed spacing was established to determine the working parameters in the seed feeding process. The results showed that the spacing between two adjacent seeds decreased significantly, with the increase in operating speed, and the decrease in seeding spacing. The external interference during seeding was more likely to cause a sharp deterioration of seeding performance. According to the previous linear seeding theory, a specific mechanism was constructed from the seed top to avoid in-depth adsorption and push the seed to the end of the dial finger fixed-point seed. A terminal release and linear seeding mechanism was then developed to cooperate with the seed plate, linear seed pushing device, and gradual choke parts of the seed disk. The action range of the progressive seed-disk gas barrier was determined, together with the active surface parameters and the parameter equation. Finally, the key parameters were determined for the terminal dial-off gas barrier. The high-speed camera technology and ProAnalyst motion analysis software were also used to compare the motion characteristics of the seed dropping process. The results showed that the terminal dial-off and linear seed falling mechanism performed better, where the seeds were uniformly accelerated in the vertical direction, while, the seed speed was 0 in the horizontal direction, and at the working speed of 12 km/h, the time interval of the seeds from the plate was approximately 0.075 s, and the vertical velocity to the seed tube was approximately 1 325 mm/s. Specifically, the seeds were detached from the seed tray when reaching the seed dropping position, in order to accelerate into the seed tube in the vertical direction in a straight line, indicating the uniform and consistent linear seed dropping. At the same time, a bench comparison test was conducted to verify the performance of the improved maize precision metering device with the air suction, terminal dial-off, and linear seeding at all operating speeds. The qualified index of seeding spacing at the high speed increased by 1.61 percentage points at the working speed of 14 km/h, whereas, the missing seeding index and the coefficient of variation of seeding spacing were reduced by 1.00, and 1.79 percentage points, respectively, compared with the ordinary choke seeding. It indicated that the terminal dial-off and linear seeding mechanism effectively improved the seeding performance at a high working speed. Finally, the field tests were conducted under a working speed of 12 km/h or less. It was found that the qualified index of seeding spacing was greater than 94%, the missing and multiple seeding indexes of seeding spacing were less than 5%, and 2%, respectively, where the coefficient of variation of seeding spacing was less than 20%, indicating the better seeding performance to fully meet the requirements of precision seeding. The terminal dial-off and linear seed falling mechanism can be expected to balance the seeding position and transverse movement of seeds, in order to greatly improve the seeding performance at the increasing operation speed. The findings can also provide a strong reference for the feeding performance of the air-suction high-speed precision metering device.