The invention belongs to the technical field of detection, and specifically relates to a method for detecting the formaldehyde content of the indoor air. The method mainly comprises the steps of sample collection, standard curve establishment, sample processing, spectrophotometry measurement, data processing and the like. According to the invention, samples are collected in a vacuum bottle for sampling, and the vacuum bottle is loaded with a gas flowmeter, so that the sampling volume can be accurately controlled; and the same sampling point is sampled twice, and the concentration change of thesame sampling point in closed and ventilation environments is measured, so that a treatment scheme can be provided for the polluted room with standard exceeding formaldehyde, for example, activated carbon can be placed at the sample point with little change before and after the ventilation, and thus the indoor formaldehyde pollution can be controlled accurately and effectively.