In view of the technical problems of long swelling time and weak water dilution resistance of gel plugging agent in drilling engineering，the pressure sensitive self-healing plugging agent CMC-DAS was prepared from carboxymethyl chitosan （CMC）and dialdehyde starch（DAS）by cyclic freeze-thaw method. The molecular structure and particle size distribution of CMC-DAS were characterized and determined respectively by means of infrared spectroscopy and laser particle size analyzer，and its swelling performance，water dilution resistance performance，pressure-sensitive self-healing performance，nano-micron pore sealing performance，pressure penetration performance and microscopic morphology were investigated. The results showed that after high-temperature aging，CMC-DAS particles were still in nano-micron monodisperse state. The water absorption swelling expansion of CMC-DAS increased first and remained stable，the swelling equilibrium time was 7 h，and the water dilution resistance was controlled within 10% after 72 h. When the pressure increased from 2.5 MPa to 10 MPa，the fracture strength of CMC-DAS increased from 0.1131 MPa to 0.3516 MPa，and the elongation at break increased from 135% to 260% . When the addition amount of CMC-DAS was 0.5%，the reduction rate of core permeability reached more than 80%，exhibiting excellent plugging performance. By comparing the microscopic morphology of CMC-DAS on the core surface before and after aging at 160 ℃ for 16 h，the gel particles could be squeezed and deformed and enter the pores and fractures of the core，and a smooth and flat isolation film was formed on the surface，which played a positive role in improving the stability of wellbore.