Through the analysis of analytical signal concept, we point out that the analytic signal of potential field data is in fact the analytic signal of gradient data. As potential field gradient components meet 2-D Hilbert transform, we propose the concept of Direct Analytical Signal (DAS) to expand total gradient method. DAS of potential field or its 2-D Hilbert transform has geophysical implication, especially for the gravity anomalies or magnetic anomalies at the pole. Based on the concept of DAS, we also propose direct analytical signal enhancement methods including the amplitude of DAS, the horizontal component of DAS, improved Tilt angle and improved Theta map. Theoretical models and digital aeromagnetic data processing show that the method can be effective for enhancing large-scale potential field data mapping.