The invention discloses a method for pre-
thinning of
undaria pinnatifida. The method is characterized by comprising the following steps: before the
seedling clamping operation of
undaria pinnatifida,taking a temporary-breeding
seedling rope and counting the
undaria pinnatifida seedlings with a length of 0.3 cm or above on the
seedling rope; marking the number as A seedling / cm which means each 1 cm of the seedling
rope is provided with A undaria pinnatifida seedlings; then taking the seedling rope out from sea water; slamming and
punching the seedling rope on a
cutting board or a ship board, so that a part of the undaria pinnatifida seedlings are dropped from the seedling rope; then placing the seedling rope back to the sea water for washing, and removing the seedlings which are separatedfrom the seedling rope; then counting the undaria pinnatifida seedlings with a length of 0.3 cm or above on the seedling rope; marking the number as B seedling / cm; and ensuring that the ratio of B toA is (0.4-0.7):1, finally using the seedling rope for seedling separation operation, and carrying out raft cultivation.