We has designed, fabricated, and measured a Single flux quantum (SFQ) toggle flip-flop (TFF). The TFF is widely used in superconductive digital electronics circuits. Many digital devices, such as frequency counter, counting ADC and program counter be used TFF Specially, a program counter may be constructed based on TFF We have designed the newly TFF and obtained high bias margins on test. In this work, we used two circuit simulation tools, WRspice and Julia, as circuit optimization tools. We used XIC for a layout tool. Newly designed TFF had minimum bias margins of +/- $37\%$ and maximum bias margins of +/-$37\%$(enhanced from +/- $37\%$). The designed circuits were fabricated by using Nb technology The test results showed that the re-optimized TFF operated correctly on 100kHz and had a very wide bias margins of +/- $53\%$.