The invention relates to the field of shell type preparation of investment casting, in particular to a surface layer shell type preparation method capable of effectively improving a small-size concaveprofile rising. The preparation method comprises the following steps that a coating is prepared, specifically, a first coating is prepared, specifically, 1 part of silica sol, 0.5-1 part of water, 2.5-3.5 parts of an aggregate, 0.001-0.005 parts of a wetting agent in part by weight are prepared, sequentially added into a first batching barrel, and uniformly stirred to form the first coating; a second coating is prepared, specifically, 1 part of the silica sol, and 2.5-3.5 parts of the aggregate in part by weight are prepared, sequentially added into a second batching barrel, and uniformly stirred to form the second coating; a wax mold is pre-coated; and shell manufacturing is carried out. The first coating with low viscosity and low surface tension is used for pre-coating and treating thewax mold, so that a wet pre-coating layer is formed between a surface layer coating and the wax mold, the direct contact between the surface layer coating and the wax mold is avoided, the phenomenonof the bubble accumulation on the small-size concave profile of the wax mold due to the oversized surface tension of the surface layer coating can be avoided, and the rising of a casting is effectively reduced.