Abstract: Since there exists about 3dB envelope fluctuation phenomenon in the traditional base band IJF coding, this disadvantage will directly affect the performances of modulation.An IJF coding type with better performance and smaller margin fluctuation is proposed in this paper.It is obtained through analyzing the generating principle of IJF signal coding type and weighting the base band pulse appropriately.Theory analysis and a large number of simulations prove that the IJF coding woks better which has narrow spectrum, higher rolling speed, continuous and gentle phase path, etc.greatly improving the performance of signal modulation.