The invention discloses a ballastless track CA mortar layer disease detecting method and device, and relates to the technical field of railway engineering. The method comprises the following steps that a space sampling sequence of a CA mortar layer is determined according to a dielectric constant of a testing wire on a ballastless track plate and a thickness of the ballastless track plate; an initial sequence of the space sampling sequence is determined through wavelet analysis, size coefficients of the space sampling sequence and wavelet coefficients of the space sampling sequence are filtered to obtain filter size coefficients of the space sampling sequence and filter wavelet coefficients of the space sampling sequence, and the filter size coefficients of the space sampling sequence and the filter wavelet coefficients of the space sampling sequence are reconstructed to form a reconstructed sequence; and a disease position of the CA mortar layer is obtained according to the reconstructed sequence. Through the method, the disease position of the CA mortar layer can be quickly detected.