The invention relates to a method for growing a large size non-linear optic crystal through the linkage of a crucible and a seed crystal. In the growth process of growing the non-linear optic crystal through a molten salt method, the seed crystal is placed in a fused mass or on the surface of the fused mass; and the seed crystal and the crucible rotate synchronously and oppositely according to a certain rotation period. A device comprises a crystal growth device and a controller capable of driving the seed crystal and the crucible to rotate synchronously and oppositely according to the certain rotation period. The synchronous and contrarotational rotation period comprises the following steps: rotating acceleratively, rotating at a uniform speed, rotating deceleratively and stopping rotation in turn in a first direction; and then rotating acceleratively, rotating at a uniform speed, rotating deceleratively and stopping rotation in turn in a second direction opposite to the first direction. The synchronous and contrarotational rotation of the seed crystal and the crucible with an adjustable rotating speed facilitates the impurity removal in an early growth period of the seed crystal, grows a single crystal with a regular shape, and reduces or even eliminates the risk of the breaking of the seed crystal caused by an oversize moment resulting from the overweight of the seed crystal.