The invention discloses a latent fault pre-warning method and device for a distribution transformer. The method and the device are specially used for online measurement and data processing of current and voltage of the distribution transformer, a short-circuit impedance calculated value reflecting distribution transformer winding deformation fault and a no-load loss calculated value reflecting distribution transformer core fault are acquired, then the calculated values and a distribution transformer factory default are compared to evaluate the operation state of the distribution transformer, a latent fault is found timely, fault pre-warning is performed, and safety operation of equipment can be ensured.