In the last decades, there has been a growing interest in microalgae due to its broad application scope. Therefore, finding a cost-effective, high yield solution for harvest. In this study, the effectiveness of a new N-rich porous triazine based organic polymer (TrzPOP) was synthesized by the reaction between cyanuric chloride and diethylenetriamine in anhydrous 1,4-dioxane. The TrzPOP is showed high BET surface area (790 m² g⁻¹) and pore volume 1.3 cc g⁻¹ for removal of blue-green microalgae. The results demonstrated that the TrzPOP had a positive zeta potential in neutral pH and harvesting efficiency (HE) of microalgae (1.8 g/L) with above 98 % at a dose of 30 mg/L of it. To reusability and easy separation from the wastewater TrzPOP nanoparticles were functionalized by Fe₃O₄@SiO₂, which results show that the synthesized Fe₃O₄@SiO₂-TrzPOP nanocomposite has a positive zeta potential in acidic pH. The magnetic removal blue-green microalgae (1.8 g/L) at a dose of 40 mg/L of nanocomposite in acidic medium was as same as harvesting efficiency of TrzPOP. The collecting procedure significantly enhanced and less than 2.0 % of microalgae cells were left after just 1 min complete separation of microalgae from paramagnetic functionalized nanoparticles were enabled through the ultrasonic method and Fe₃O₄@SiO₂- TrzPOP was recycled up to five times successfully.