The invention belongs to the technical field of continuous casting, in particular to a secondary cooling method for controlling cross cracks in a corner of a microalloy steel slab. The method comprises the steps of controlling the temperature in the corner of a casting blank by a weak cooling mode after the crystal of the casting blank occurs and before the casting blank is separated from a bending section, so the temperature of the corner of the casting blank is not lower than Ae3 temperature which is the highest temperature at which austenite and ferrite coexist under the balance state; changing the weak cooling mode into an intensified cooling mode before the casting blank enters a straightening section, so the temperature of the corner of the casting blank achieves the Ar3 temperature, namely the temperature at which the austenite begins converting to the ferrite in the cooling process of the casting blank; after the casting blank enters the straightening section, continuously using the intensified cooling mode. The secondary cooling mode control of the continuous slab is optimized, and educts with larger dimension and more dispersed distribution are obtained by the weak cooling mode firstly, so the plasticity of the casting blank is greatly increased; then the transgranular ferrite with large proportion is obtained by the intensified cooling mode, the stress is reduced, the occurrence probability of cross cracks in the corner of the casting blank is greatly reduced, and the method is simple and easy to realize.