The invention discloses an omnidirectional antenna synthesis system, so as to solve the problems of inaccurate phase and amplitude control when omnidirectional beam transmission is formed for a directional antenna and signals are transmitted to four channels of the antenna. A transceiver comprises four transmitting channels and four receiving channels connected with a 0-DEG antenna, a 90-DEG antenna, a 180-DEG antenna and a 270-DEG antenna of the directional antenna through transmitting and receiving switches respectively. A DA sampling clock has a frequency of 400MHz, an 80MHz transmitting digital intermediate frequency is outputted, an AD sampling clock has a frequency of 100MHz, A 120MHz intermediate frequency is sampled and received, transmitting and receiving both adopt one-time variable frequency, and each channel has a simple structure. The overall machine adopts one reference clock, transmitting signals and receiving signals are ensured to have the same source, and frequency difference elimination and phase calibration are facilitated. An MCU and an FPGA together complete amplitude/phase control on the transmitting antenna, and antenna omnidirectional synthesis is realized.