In this paper, we propose a novel control technique, named as periodically intermittent discrete observation control (PIDOC), to investigate the synchronization issue of fractional-order coupled systems. Distinguished from periodically intermittent control which is widely applied in control fields, PIDOC proposed in this paper adopts discrete-time state observations in work time during a control period. In this way, PIDOC is more reasonable and available than traditional periodically intermittent control based on continuous-time state observations. Moreover, different from previous work about synchronization of fractional-order coupled systems, coupling term considered in this paper is nonlinear, which is more general. Then, combining graph theory with Lyapunov method, several synchronization criteria are obtained. Next, we successfully employ PIDOC to investigate synchronization of unified fractional-order chaotic coupled systems. Finally, two numerical simulations are presented to verify the validity of our theoretical results and the effectiveness of control scheme.