The invention relates to the technical field of nondestructive testing of pouring quality of a ballastless track functional layer of a high-speed railway, especially to a ballastless track functionallayer defect imaging method, thereby overcoming defects of inaccurate geometric dimension estimation and defect imaging of the existing recognition method in the prior art. The method comprises the following steps: step a, acquiring an echo signal Burg power spectrum under the condition of enabling k to be equal to 100; step b, calculating a ratio eta of a [f2, f1] energy spectrum to total echo energy; step c, ranking the ratio eta in a descending order, expressing possible defect points Pi by using the top 10% value as an initial value under the condition that the i is equal to 1, ... , and q, and initializing the i to be equal to 1; step d, carrying out breadth searching on an edge echo frequency distribution mode by taking the Pi as a center, using an area from the point to the edge asR(Pi) under the condition of existing the edge echo frequency distribution mode, and otherwise, not recording the point; step e, enabling the i to be equal to the sum of the i and 1; ending the searching under the condition that the i is larger than q; and otherwise, returning to the step d to carry out searching continuously. The ballastless track functional layer defect imaging method has advantages being free of damage and high in precision and is suitable for accurate imaging of the internal defects of the ballastless track functional layer.