The circuit structure and noise characteristics of a high-speed spatial coherent balanced detector were analyzed, and the dependence of key technical parameters on the circuit structure of the balanced detector was clarified. Two kinds of high-speed spatial balanced photoelectric detectors were designed by using resistance sampling and double TIA (Transimpedance Amplifier) synthesis, and their performance parameters were verified by experiments. The experiments indicate that both kinds of high-speed coherent detectors can be used for high-speed coherent detection, while the detection sensitivity and anti-noise performance from the double TIA voltage synthesis balanced detector are better than those from the resistance sampling type detector. When the communication rate is 5Gbps and the bit error rate is 10-8, the optimal detection sensitivity of resistance sampling type balanced detector is -33.51 dBm, and that of the double TIA synthesis balanced detector is -43.4 dBm, higher nearly 8dB than that of the Discovery's 5Gbps balanced detector. The research on the structure of high-speed spatial coherent photodetector provides a theoretical basis for the establishment of a high-sensitivity and high-speed spatial coherent optical communication system.