The experimental measurements reveal that a notable characteristic of the imaging neutral particle analyzer (INPA) passive signal in Experimental Advanced Superconducting Tokamak is its bimodal distribution in the pitch angle (). The synthetic images of INPA passive signal, obtained through synthetic diagnostic, are in good agreements with the experimental images. The measurements reveal two distinct pitch peaks in the passive signals. The synthetic diagnostic results indicate that the two observed pitch peaks predominantly originate from fast ions with distinct initial deposition locations: the low pitch peak arises from particles initially deposited on the low-field side, while the high pitch peak corresponds to those initially deposited on the high-field side. Furthermore, experimental observations demonstrate that the change of the electron density, which directly affects the initial deposition distribution of fast ions, leads to variations in the ratio between these two pitch peaks. Within similar electron density ranges, the proportion of high pitch peak increases with elevated , indicating the increasing fraction of fast ions. The variation in the ratio between two pitch peaks is observed during long-lived mode, further reflecting the relationship between fast ions and bimodal distribution. During supersonic molecular beam injection, the passive signal intensity exhibits an order of magnitude amplification while preserving the two pitch peaks. INPA passive signals, which carry information about the fast ions’ distribution, can serve as a novel diagnostic for inferring fast ions transport.