To ensure electric energy supply at arbitrary directions, omnidirectional Wireless Power Transfer (WPT) system is gaining increasing attention. The cubic structure with three orthogonal coils is becoming one of the optimal technical solutions for omnidirectional WPT system. In this paper, the transfer characteristics, such as load resistance changing and coupling coefficient changing, of a three-transmitter and three-receiver WPT system are analyzed and compared with those of a conventional single-transmitter and single-receiver WPT system. According to the electric circuit theory and 1:1 WPT system model, the theoretical model of M:N WPT system is derived and generalized. And then, a set of 3D orthogonal coils is designed and trial-manufactured for testing the transfer characteristics of the 3:3 WPT system. At last, an experimental platform is built up to test and compare the transfer characteristics of both 1:1 and 3:3 WPT systems. The tested results show that the theoretical analysis is correct and the maximal transmission power is 150W and the maximal transmission efficiency is 43.6% when the 3:3 WPT distance is 20cm. Furthermore, the designed 3:3 WPT system can realize full-space energy transmission for electronic equipment and the output stability can maintain high when the coil spatial offset occurs.