Spin-exchange relaxation free（SERF）atomic magnetometer is a kind of ultra-sensitive magnetometer, and its miniaturization is very important for the application of magnetometer. The layout of optical path is the key factor that restricts its size and sensitivity. In this paper, a single beam miniaturized atomic magnetometer is designed. The magnetometer is a cylinder with a diameter of 21.2 mm and a height of 40.5 mm. Thermal simulation experiments are carried out on the magnetometer. The experimental results show that the design is reasonable in structure and easy for multi-channel measurement, and has practical application value in the field of biological magnetic field measurement such as magnetoencephalography and magnetocardiogram.