The invention relates to the technical field of metallurgy steelmaking sheet billet continuous casting, in particular to a method of preventing transverse corner cracks of a microalloyed steel continuous casting sheet billet. After the method is applied in a ladle furnace smelting technology and a continuous casting technology, the mass percent of Ti in microalloyed steel is controlled at 0.018-0.025%, and a specific water flow of secondary cooling water of a continuous casting machine is adjusted to 0.42L/kg. According to the method, the problem of the transverse corner cracks of microalloyed steel continuous casting sheet billet is mainly solved by adopting a technological means; through molten steel micro-Ti treatment, the grain boundary precipitation of NbN and VN in the microalloyed steel and the grain boundary strength are reduced and weakened, a third high-temperature brittleness area of steel is avoided from a cooling procedure, and the stress strain of corners of the casting billet during straightening is reduced; no additional equipment transformation or investment is required; no strict requirement is made on whether electromagnetic stirring equipment is equipped; and the method is low in investment and wide in application range, and has few restrictions.