The invention discloses a plot experiment seeding machine comprising a rack, a land wheel, furrow ploughs and seed metering and replacing devices, wherein each seed metering and replacing device comprises a first seed metering plate, a fixed plate, a seed metering cavity, a seed metering core and a seed discharging core; a plurality of seed holes are formed in the first seed metering plate; seed metering holes of which the upper ends correspond to the seed holes are formed in the fixed plate; a seed inlet connected with the seed metering holes through a seed metering funnel is formed in the top of the seed metering cavity, a seeding outlet and a seed discharging outlet are formed in the bottom of the seed metering cavity, the seeding outlet is connected with a seeding channel located at the rear of the corresponding furrow plough, and the seed discharging outlet is connected with a recovery device; the seed metering core is arranged in the seed metering cavity and is provided with a seed metering groove located between the seed inlet and the seeding outlet; and the seed discharging core is arranged in the seed metering cavity in a way of being parallel to the seed metering core, corresponds to the seed discharging outlet and is provided with a seed discharging hole. The plot experiment seeding machine is capable of automatically switching different varieties of crop seeds and regulating the row spacing, simple in structure, flexible in operation and relatively low in manufacture cost.