The utility model discloses a formaldehyde concentration monitor. The monitor comprises a microprocessor circuit and a power circuit; the input terminal of the microprocessor circuit is connected with a keyboard input circuit for setting parameters of the monitor, and a signal conditioning circuit; the input terminal of the signal conditioning circuit is connected with a formaldehyde sensor; the signal conditioning circuit amplifies, filters and zeros signals sampled by the formaldehyde sensor, and then outputs the signals to the microprocessor circuit; the microprocessor circuit converts A/D and calculates the concentration of the signals processed by the signal conditioning circuit, and outputs the signals to a LCD display circuit connected with the output terminal of the microprocessor circuit and used for displaying the monitoring information in real time, an acoustic-optic alarming device alarming when the formaldehyde concentration exceeds the standard, and a communication circuit; and the communication circuit receives the signals processed by the microprocessor circuit and transmits the signals to an upper computer connected with the output terminal of the communication circuit and used for storing the monitoring information in real time. The monitor has the advantages of simple structure, reasonable design, reliable operation, low cost, and convenient popularization and application.