To solve the problems of high noise and obvious drift in long-term observation of proton vector magnetometer, obvious temperature effect of fluxgate magnetic field meter and large investment in thermal insulation magnetic room, a seismic geomagnetic vector measurement system based on the optically pumped cesium magnetometer is developed. In this article, the measuring principle and instrument structure are introduced in detail, the mixed-component coil device is designed, and the stability is analyzed. The prototype is tested at the Mengcheng seismic station. The results show that, during the experimental period, the instrument records well, the sampling rate of the experimental instrument reaches 1 Hz, the monthly noise of the total intensity, the horizontal component and the magnetic declination in January are 0. 01 nT, 0. 02 nT and 0. 003′, respectively, which are obviously superior to the best noise level of proton vector magnetometers of seismic geomagnetic observation basic network. They are also better than the noise level of two fluxgate magnetic field meters at the same venue and the average noise level of the seismic geomagnetic observation reference network. The maximum drift of the horizontal component and the magnetic declination are 1. 3 nT and 0. 16′, respectively, which is less than the baseline drift of the pedestal-clock proton vector magnetometer, so good stability can be obtained.