This paper investigates the problem of synchronization for offset quadrature amplitude modulation based orthogonal fre-quency division multiplexing (OFDM/OQAM) systems based on the genetic algorithm. In order to increase the spectrum efficiency, an improved preamble structure without guard symbols is derived at first. On this basis, instead of deriving the log likelihood function of power spectral density, joint estimation of the symbol timing off-set and carrier frequency offset based on the preamble proposed is formulated into a bivariate optimization problem. After that, an improved genetic algorithm is used to find its global optimum so-lution. Conclusions can be drawn from simulation results that the proposed method has advantages in the joint estimation of syn-chronization.