A novel 1×2 polymer electro-optic (EO) switch based on seven vertical-turning serial-coupled microrings is proposed for dropping crosstalk and obtaining flat boxlike spectrum. The device structure, theory and formulation are presented, and the microring resonance order and coupling gaps are optimized. The switching voltage of the device for obtaining crosstalk lower than ?30 dB under through state is decided to be about 1.86 V. Under the operation voltages of 0 V (drop state) and 1.86 V (through state), the switching performance is characterized, and the output spectrum is analyzed. The calculation results show that the crosstalk at through state and that at drop state are ?30.2 dB and ?53.2 dB, respectively, while the insertion losses are 0.86 dB and 3.18 dB, respectively. Owning to the seven serial-coupled microrings resonance structure, the proposed switch reveals the favorable boxlike spectrum compared with the simple device with only one microring, and thus the crosstalk under drop state is improved from ?26.8 dB to ?53.2 dB. Due to the low crosstalk, this device can be used in optical networks-on-chip for signal switching and routing.