The invention relates to a tower solid-liquid premixing device and a premixing method thereof; solid power and liquid can be uniformly mixed in certain proportion through the device and the method, so the premixing device and method are particularly applicable to the uniform mixing of solid powder and liquid with high viscosity after mixing. The tower solid-liquid premixing device comprises a mixing system 1010, a stirring separation system 1020 arranged in the mixing system 1010, a high pressure gas spraying system 1030, a storage system 1060, a feeding system 1040 and a discharging system 1050 respectively arranged on the top and bottom of the mixing system 1010. The mixing system 1010 is a cylindrical tower mixing reactor enclosed by a casing 101, the tower mixing reactor is provided with a vertical rotary shaft 103 positioned at the center of the casing 101, the rotary shaft 103 drives the stirring separation system 1020 connected with the rotary shaft to rotate for mixing solid and liquid materials.