As the key module of fractional N PLL(Phase Locked Loop), the Sigma Delta modulator can significantly improve the performance of the fractional N PLL by the way of noise shaping. However, when it comes to the three most important specifications: the output sequence cycle, the range and the error, the now existing modulators cannot improve them at the same time. As a contrast, the proposed novel Sigma Delta modulator ameliorates the aforementioned three specifications simultaneously by adding a feed forward between two adjacent stages and adjusting the modulus of adders to prime number. Regardless of the input value and initial conditions, the presented modulator guarantees a sequence length of M3, which is almost M2/2 times of that in traditional modulator, where M is the largest prime number smaller than 2n0, and n0 is the bit width of adders. The simulation results show that, compared with the existing modulators, the proposed modulator can effectively remove the spur in the output spectrum and make it more close to the ideal Sigma Delta modulator.