Reports about fluorescent sensors for the highly sensitive and selective detection of Ni²⁺ are rare compared with Hg²⁺, Ag⁺, Cd²⁺, Pb²⁺, Cr³⁺, etc. Herein, we report the synthesis and application of two conjugated polymer fluorescent sensors, P-1 and P-2, using benzochalcogendiazole and triazole as cooperative receptors of Ni²⁺. The synthesis was carried out by the polymerization of 4,7-diethynylbenzoselenadiazole (M-2) and 4,7-diethynylbenzothiadiazole (M-3) with 2,7-diazido-9,9-dioctyl-9H-fluorene (M-1)via copper-catalyzed azide–alkyne cycloaddition. P-1 and P-2 exhibit emission peaks at 535 nm and 514 nm, and show yellow and green fluorescence, respectively. These two polymers showed outstanding fluorescence response behavior toward Ni²⁺ during real-time detection. Compared with benzothiadiazole-based P-2, benzoselenadiazole-based P-1 showed higher sensitivity and selectivity, and its detection limit could reach 2.4 nM, which might be due to the specific electronegativity of selenium. This work increases the application scope of the click reaction in regard to the design and synthesis of novel conjugated polymer fluorescent sensors based on the benzochalcogendiazole unit.