The utility model relates to a sleeve mixer which comprises an inner pipe (1), an outer pipe (2) and an annular gap (3) between the inner pipe and the outer pipe. The sleeve mixer is characterized by further comprising a sleeve outlet elbow pipe (4) and a blocking plate (5), the sleeve outlet elbow pipe (4) is connected to the outlet end of the outer pipe (2), and the blocking plate (5) is located in the annular gap (3) between the inner pipe (1) and the outer pipe (2). The sleeve mixer can be connected with a flash evaporation kettle lateral wall flange (12) and is of a double-layer sleeve mixer structure, the problem of chloromethane hydrolyzing in the existing prior can be effectively solved, and steam stripping and dissolution can be finished at the same time.