In conclusion, we have developed a highly sensitive luminescent porous organic polymer probe TAPB-BTDD for ultrasensitive detection of Pd²⁺ in aqueous solution. The results manifested that TAPB-BTDD is a typical turn off sensor and possesses high sensitivity and specificity for Pd²⁺. A linear curve was achieved when measured in the range of 100–900 μM (F₀/F = 0.7585 + 0.0075 [Pd²⁺], correlation coefficient R² = 0.9912). The LOD was determined to be 0.54 μM for Pd²⁺ in methanol/H₂O solution, and the other ions showed no interference effect. In addition, TAPB-BTDD showed basically unchanged emission intensities and rapid response to Pd²⁺ after eight recycling tests, suggesting that the POP has high stable recycle repeatability. More importantly, this work highlights that imine-based porous organic polymer is an ideal candidate for fluorescent probe for ultrasensitive detection of heavy metal ions.