ABSTRACT ObjectiveTo evaluate the M and two-dimensional ultrasound used in diaphragmatic contraction movement in patients with myasthenia gravis crisis，and to explore the application value of two kinds of ultrasonic measurement in diaphragm movement. Methods The study enrolled 38 patients with myasthenia gravis crisis （MC） in our department of Neurology，including 11 males and 27 females from January 2016 to December 2017 . At the same time，38 healthy people with similar height，weight and age were selected as the control group. The thickness of inhale and exhalation end of bilateral diaphragm was measured respectively by two-dimensional ultrasound，and then the thickness of the thickness and thinnest of bilateral diaphragm sampling line was measured by M-mode ultrasound，and the change rate of diaphragm contraction was obtained by calculating（Δtdi%）. Results The two methods of two-dimensional ultrasound and M ultrasound showed that the change rate of diaphragmatic contraction was significantly higher than that of group MC （P=0.000），and the difference was statistically significant.In the normal control group，there was no significant difference in the difference of the bilateral diaphragmatic Δtdi% between the two methods of ultrasonic measurement. In group MC，there were significant differences in the difference of the right diaphragmatic Δ tdi% between two methods （r=0.937，t=3.038，P=0.004<0.05）. Conclusion This study shows that ultrasound can measure the diaphragmatic contraction ofΔ tdi%，which can be quantified to evaluate the contractile function of the diaphragm and to be used to observe the changes of diaphragmatic function in MC patients. In MC patients，M ultrasound can better reflect the changes in the contractile function of the diaphragm than the two-dimensional ultrasound.