A coring inner-tube of flexible retractable and foldable pipe (bag) has been developed to solve the problems caused by rigid coring tube, such as core disturbance, moisture retention and low core recovery. By the comparison of influence on coring effects by the flexible coring tube with axial and radial folding patterns, the axial one was selected. The flexible coring inner-tube is made of polyethylene plastic with glass wool, and employs the drilling technology with ancillary techniques of high matrix bottom jet bit and single way claw spring cover. In the tests of 4 typical drilling projects, the sample disturbance are lower than 5%, moisture retention higher than 95% and core recovery reaching 80%～95%. The practices show that by the triple-tube equipped with coring inner-tube of flexible retractable and foldable pipe (bag), special rock samples and the undisturbed samples can keep high fidelities and high recovery with perfect coring effect.