The invention provides a method for preparing a transparent sensor for structural crack monitoring based on the self-assembly of a gas-liquid interface. The invention relates to the method for preparing the transparent sensor for structural crack monitoring. The invention aims to solve the defects that a toxic organic solvent is used and the treatment process is complicated in the prior art. According to the method, SWCNTs are not purified, no toxic organic solvent is used, the environmental protection is greatly improved, and the large-area preparation can be easily realized. Based on the L-Btechnology and a self-assembly method, a SWCNTs conductive network with uniform distribution is prepared at the gas-liquid interface by using van der Waals force between carbon nanotubes and the thrust of a SDBS aqueous solution, the conductive network is transferred to a PDMS substrate by a pick-and-pull method to prepare a transparent conductive SWCNT film with a sandwich structure, and in themonitoring process, when a power supply is abnormal, since the sensor of the invention is transparent, the width of a crack can be visually observed. The method is used in the field of sensors.