A serial port connection circuit comprises a first and a second photoelectric couplers, wherein an anode of a light emitting device of the first photoelectric coupler is connected with a first power supply, and a cathode thereof is connected with a transmitting terminal of a first chip, a collector of a light receiver of the first photoelectric coupler is respectively connected with a second power supply and a receiving terminal of a second chip, an emitter of the light receiver of the first photoelectric coupler is grounded, the anode of the light emitting device of the second photoelectric coupler is connected with a second power supply, and the cathode thereof is connected with the transmitting terminal of the second chip, the collector of the light receiver of the second photoelectric coupler is respectively connected with the first power supply and the receiving terminal of the first chip, the emitter of the light receiver of the second photoelectric coupler is grounded. The serial port connection circuit can easily achieve electrical signal transmission with light medium by using the low-cost photoelectric coupler, thus improving the voltage level at both ends of the photoelectric coupler, effectively isolating crosstalk between the signal transmitting terminal and the receiving terminal, and greatly improving signal quality.