Abstract: This paper is to study the feasibility of liquid penetrate testing of tiny defects from the point of view of the testing principle, physical properties of liquid penetrate testing, dry imaging agent imaging characteristics, tiny defect detection ability and the feasibility of on-site inspection process. Experiments show that increasing in osmotic dropping time,　prolonging the imaging time appropriately, and　increasing the vibration and preventing the water washing when necessary can improve the detection rate of tiny flaws in the liquid penetrate test.