National Natural Science Foundation of China [51305371, 51305373]; Natural Science Foundation of Fujian Province [2013J05083]; Ph.D. Programs Foundation of Ministry of Education of China [20120121120035] ; AC pulse-modulated electrohydrodynamic direct-writing (EDW) was utilized to direct-write orderly micro/nanofibrous structure on the flexible insulating polyethylene terephthalate (PET) substrate. During the EDW process, AC electrical field induced charges to reciprocate along the jet and decreased the charge repulsive force that applied on charged jet. Thanks to the smaller charge repulsive force, stable straight jet can be built up to direct-write orderly micro/nanofibrous structures on the insulating substrate. The minimum motion velocity required to direct-write straight line fibrous structure on insulating PET substrate was 700 mm/s. Moreover, the influences of AC voltage amplitude, frequency, and duty cycle ratio on the line width of fibrous structures were investigated. This work proposes a novel solution to overcome the inherent charge repulsion emerging on the insulating substrate, and promotes the application of EDW technology on the flexible electronics.