In order to verify the effectiveness and practicability of splitting grouting reinforcement method in treating collapsible loess foundation in northwest China，and to guide the safety construction，firstly，the split grouting field experiment was carried out on the site where the reinforced building is located. After 56 days，static load tests were carried out on the natural foundation and the grouting composite foundation. On this basis，a 30-day immersion test was carried out to collect the raw data such as grouting micrographs，bearing capacity and collapsibility. According to the test results，combined with the on-site building，the same materials and test methods were used to correct the tilting and reinforce the building. The results showed that: under the condition that the maximum pressure of primary grouting was 0.3 MPa and the maximum pressure of secondary grouting was 0.6 MPa，the method of split grouting with steel tube with mass ratio 1 ∶ 1 cement slurry and split grouting in two layers showed a good splitting effect. The bearing capacity of the loess foundation strengthened by splitting grouting method was nearly three times higher than that of the original foundation，which greatly improved the engineering properties of the loess. After grouting，more than 67% loess collapsibility could be effectively eliminated. The building underwent uniform settlement and had good stability. In addition，a new settlement calculation method based on pile-soil stress ratio for composite foundation with small pile diameter was proposed.