In order to find an easily usable, practical and objective model to assess soil productivity in Wulanchabu City, the author modified PI model (MPI-Ⅱ) based on the PI model and existing modified PI model (MPI). Considering the soil characteristics of study area, the calculation method of suitability index of organic matter of MPI was improved, meanwhile, CaCO3 content was added to MPI-II model as a new parameters. Firstly, the author selected soil species in study area to assess their productivity index using the MPI model and MPI-Ⅱ separately. Then, simulated results were compared with the assessed value by comprehensive assessment method which was used in the second soil survey. The results showed that: (1) the determination coefficient between the calculation value of MPI-Ⅱ model and comprehensive assessment method with R2=0.589 (P<0.01) was higher than that between the calculation value of MPI model and comprehensive assessment method with R2=0.305 (P<0.01), which meant that the calculation value of MPI-Ⅱ was more closer to the real situation in the study area; (2) Generally speaking, the calculation value of MPI-Ⅱ model was compatible with comprehensive assessment method except that 5 soils showed obvious difference between them, most probably due to the subjective of comprehensive assessment method. In conclusion, the MPI-Ⅱ model was more suitable than MPI model for the productivity assessment in Wulanchabu City.