Morphology regulation is an effective strategy for improving the sensor sensitivity of transition metal oxide nanostructures. In this work, SnO₂ with three different morphologies (nanorods, nanoparticles, and nanopillars) has been synthesized by a simple one-step solvothermal process with the addition of various solute ratios at 180 °C for 6 h for detecting HCHO at the optimum working temperature of 320 ℃. Compared to nanorods and nanopillars, the creation of SnO₂ nanoparticles exhibits a much faster response time and sensitivity than other samples, showing the fastest recovery time (18 s) with the highest sensitivity of 6 to 100 ppm HCHO gas. The sensing mechanism of the sensors is investigated by BET methods and XPS analysis, revealing that the pore size distribution and amount of O_V and O_C improve the charge transfer and HCHO adsorption of nanoparticles sensor. Such an effect of morphology control on sensing performance paves an idea for the development of different structures-based HCHO sensors.