In this thesis, several plasma wakefield-based flexible undulator/wiggler schemes have been developed for the generation of high-energy radiation. First, the plasma undulator/wiggler field can be generated by injecting a Gaussian laser pulse with a transverse offset/angle or beating several different HG-modes into a parabolic plasma channel. With a wide Gaussian pulse, the wakefield provides a linear focusing force near the propagation axis that drives the betatron oscillation of the injected electrons. The extra driving force is introduced by the centroid oscillation of the laser pulse. Surprisingly, with the HG-modes, the undulator/wiggler field becomes monochromatically sinusoidal when the strength of each mode matches a special condition. second, the dynamics of both a single electron and an electron beam are well studied to optimize the oscillation qualities. The further theoretical work indicates that the oscillation amplitude and strength for the accelerated electron beam can be sufficiently increased within the first several Rayleigh lengths of propagation by an initial resonance between the betatron and undulator oscillation. As a result, the radiation spectrum can be largely extended, for example to strong gamma-ray regime. Ultimately, the radiation spectrum from the oscillation of an electron beam is calculated. The proposed schemes are capable of generating an x-ray radiation spectrum with a narrow bandwidth or synchrotron-like x/gamma-ray radiation of high energy. It is also demonstrated that these flexible schemes can be tuned to generate radiation carrying well-defined angular momentum.