Lead halide perovskite has attracted enormous attention with its excellent photoelectric properties, while the practical applications are limited by the inherent instability and toxicity of the lead halide perovskites. Therefore, this paper proposed a lead-free copper-based perovskite Cs2CuBr4 with relatively stable performance and used its humidity-sensitive characteristics to fabricate a quartz crystal microbalance (QCM) humidity sensor based on the Cs2CuBr4 sensitive film. The results showed that when the concentration of perovskite solution was less than 0.4μg/μL, the sensitive film sensitive film had good humidity sensing performance at 11%—84% RH. Among them, the optimal concentration was 0.3μg/μL (QCM-3). When the film mass was 398.95ng, the sensor had high sensitivity (37.65Hz/% RH), excellent logarithmic linear relationship (R2=0.9948) and fast response/recovery time (5s/1s). Therefore, lead-free copper-perovskite Cs2CuBr4 had a good application prospect in humidity sensing field.