Two novel conjugated organic polymers BTTh-1 and BTTh-2 were designed and synthesized. They were prepared by the reaction of two aldehyde units with melamine. Both aldehyde units were based on benzothiadiazole. The difference between the final aldehyde units was the introduction of thiophene groups in the BTTh-2 aldehyde monomer units. The difference between the two materials in the photocatalytic degradation of tetracycline was discussed in the context of the thiophene unit. The degradation efficiency of tetracycline by BTTh-2 (90.9%) was much higher than that of BTTh-1 (40.7%). The characterization results showed that BTTh-2 has a strong charge separation ability and fast transmission rate. After light excitation, the recombination ability of photogenerated holes and electrons becomes weak, and it has better utilization ability for visible light; the bandgap width is narrower.