In order to understand the effects of different improving patterns for badly degraded Robinia pseuc-doacacia plantation in the Yellow River Delta area, soil enzyme activity, soil density, porosity, saline-alkali content and soil nutrients under the plantation improved for five years were determined. Four improving measures, including cotton field, pure forest of Fraxinuschinensis, agro-forestry of F. chinensis + cotton and mixed forest of F. chinensis + R. pseucdoacacia, were selected, with the badly degraded R. pseuc-doacaciaplantation serving as the control (CK). Results are as follows:(1) The improving patterns clearly affected soil phosphatase, urease and polyphenol oxidase, but not soil peroxidase. Soil phosphatase and ure-ase activity increased, but soil polyphenol oxidase decreased. The activities of polyphenol oxidase and urease showed such an order of mixed forest>pure forest>agro-forestry>cotton field. Phosphatase activities in mixed forest, agro-forestry, pure forest and cotton field were 3.5, 3.2, 1.7and 1.6times of that of CK, re-spectively. (2) Soil density and soil salt content decreased after adopting the four improving patterns, a nd these indexes were in the order of mixed forest