A modular gathering platform for grain harvesters is provided for coupling to the front of a grain harvester or processor which can gather plants previously prepared in one or more rows by at least one central belt conveyor with functional side by side coupling to other equal harvesting conveyor belts. The platform includes a transversal mounting structure having an internal opening, at least one central harvesting conveyor belt having front and rear extremities and two side couplings, additional harvesting conveyor belts coupled to the sides of the central belt, an anti-jamming roll and a rotating guiding roll. The central harvesting conveyor belt and additional side harvesting conveyor belts, the anti-jamming rolls, and the guiding roll are synchronized by an actuation assembly, and the guiding roll moves the harvested plants towards the exit. The platform advantageously allows for the gathering of a crop that has been prepared in rows.