The output bandwidth and the capability to generate multiple analog outputs with accurately adjustable relative phase are important specifications of arbitrary waveform generator (AWG). To increase the output bandwidth, AWG with a multi-memory paralleled direct digital synthesizer structure (DDS) was proposed to break through operating speed limitations of memory and field programmable gate array. But this structure does complicate synchronization of the analog outputs. This paper proposes a structure for synchronization of the outputs of multi-channel high speed AWG that generates arbitrary waveforms using a multi-memory paralleled DDS. Careful distribution of the clock and trigger signals enables elimination of the random initial phase caused by the frequency divider. Based on this structure, a four-channel 600 mega samples per second AWG is designed. An embedded clock synchronization calibration module is designed to eliminate the random phase difference caused by a frequency divider inside a digital-to-analog converter. The AWG provides a 240 MHz bandwidth, 16 mega-samples storage depth, inter-channel initial skew accuracy less than 150 ps, and 0.0001° phase resolution, which can be used to generate two pairs of I/Q signals or a pair of differential I/Q signals for the quadrature modulator. Additionally, more AWGs can be cascaded to obtain more output channels with an output timing skew between adjacent channels of less than 1.6 ns.