The invention relates to a glue injection flow deflector for the two ends of an assembled mullion corner brace in doors and windows. The glue injection flow deflector is characterized by comprising a glue injection flow deflector body; the glue injection flow deflector body is rectangular, small columnar jaws are arranged on the back face of the glue injection flow deflector body, and a rectangular through groove is formed in the glue injection flow deflector body. The glue injection flow deflector has the advantages that compared with the prior art, the flow deflector is arranged on the assembled corner brace, during glue injection, the purposes that the flow direction of corner assembling glue is guided and a cavity of the corner brace is blocked to block air convection can be achieved, after the flow deflector is used, the strength and sealing performance of the corners of the doors and windows are greatly improved, and more importantly, the energy-saving effect of the windows can be improved. Through the glue injection flow guide process, the situation of leakage and dew formation at the corners is completely eradicated. According to the mullion glue injection flow deflector, hard connection of the assembled corners of the doors and windows is changed into glue flexible connection, and therefore leakage can be completely eradicated from the source.