The invention relates to a filament bundle for a polylactic acid cigarette with a low filament bundle linear density, a preparation method thereof and an application thereof. The filament bundle for the polylactic acid cigarette is prepared through mixing polylactic acid master batches with titanium dioxide brightening master batches, and the filament bundle linear density, the monofilament linear density and the crispation number of the filament bundle are 0.4-1.5ktex, 2-6dtex and 20-30/25mm respectively. The filament bundle for the polylactic acid cigarette with a low filament bundle linear density can be mixed with a corresponding filament bundle (an acetate fiber filament bundle) for a cellulose diacetate cigarette to form a filter rod, so the application amount of the acetate fiber filament bundle is reduced, the insufficient situation of the filament bundle for the acetate fiber cigarette is alleviated, the cost is reduced, and the suction taste of the cigarette is maintained without a too large change. In addition, the pollution to the environment is reduced because polylactic acid has a biodegradable characteristic.