This paper propos a periodic intermittently connected-based data delivery in opportunistic networks (PICD). By effectively utilizing periodic intermittent connectivity between any two nodes, PICD can improve data delivery: First, for a certain node, based on its periodic intermittently-connected paths to the sink and its data delay tolerance, PICD establishes the delay probability model by means of random dynamic programming. Next, PICD will calculate the node's periodic delay probability distribution matrix by the function space iteration. Next, according to the node's distribution matrix, the current data delivery probability can be calculated by specifying period and tolerable delay, and this will become the key-player of the next-hop choosing. In short, the probability forwarding mechanism is delay-relevant and can increase data delivery probability within a tolerable amount of delay. Simulation shows that compared with existing algorithms, which only take advantage of single-hop delivery probability, PICD is better at data delivery and can also lower delay.