The work aims to study a new method to increase the wet strength of paper by selective oxidized fiber with sodium periodate with regard to the environmental pollution caused by the use of traditional wet strength agent. With the unbleached softwood kraft pulp as raw material, the fiber was selectively oxidized with sodium periodate. Fiber morphology analyzer and infrared spectroscopy were applied to analyze the fiber morphology and characterize the fiber, respectively. The physical characteristics of the finished paper and the paper surface morphology were analyzed and observed. After the oxidation with sodium periodate, the fiber length and width had a little change, but the fiber roughness decreased significantly. Besides, there was a large number of aldehyde groups on the fiber surface. The aldehyde groups on the fiber surface could have the condensation reaction with the hydroxy on the fiber in the process of paper formation, thus forming the hemiacetal structure. The hemiacetal structure improved the bonding strength between the fibers, thus improving the wet strength of the paper. The wet strength of paper can be improved by selective oxidized unbleached kraft pulp with sodium periodate.