In order to ensure the engineering properties of sandy pebble soil during EPB shield tunneling through the sandy pebble stratum, foam agents of different stability were added to the sandy pebble stratum with 20%, 40% and 60% pebble content under the background of Mingjiu section No.2 air shaft to Jiujiangbei section of Chengdu rail line 17. Indoor slump test, seepage test and spewing test were carried out to study the changing laws of fluidity, permeability and time-dependent nature, which reflects the adaptability between the stability of foam agent sand and sandy pebble soil. The results show that: 1)The foam agent with good stability can adapt to sandy pebble soil with less than 60% pebble content, that is, foam stability is beneficial to enlarge the application scope of sand cobble soil; 2)The foam with good stability can keep the good fluidity and impermeability in the whole process of excavating and discharging the conditioned sandy pebble soil; 3)Excessive foam mixed into the improved sandy pebble soil is easy to disintegrate, which means that the improved soil is difficult to achieve good workability; 4)The gusher pressure of improved sandy pebble soil is an important index to test the improvement effect.