Aromatic polyimides (PI) with low-dielectric constant are becoming more and more important with the continuous development of high-speed communication technology. Herein, high fluorine-containing PI with low-dielectric constant was prepared. First, a novel aromatic diamine monomer 4,4′-(3,3′-bis[trifluoromethyl]biphenyl-4,4′-diyl)bis(oxy)bis(3-[trifluoromethyl]aniline) bearing multi-trifluoromethyl groups (12FDA) was synthesized and characterized. Subsequently, a series of PI with high-fluorine content (HFPI) were obtained by two-step polymerization of 12FDA with three commercial dianhydrides. The polymer films cured at a maximum temperature of 310°C showed excellent thermal and mechanical properties with high-glass transition temperatures (>250°C) and high-storage modulus (> = 2.0 GPa). The 5% weight loss temperatures of HFPIs were all above 500°C, which indicated that HFPIs exhibited excellent thermostability. Meanwhile, HFPI exhibited low-water absorption (<0.3%) and low-dielectric constant (2.40–2.68 at 1 MHz). The excellent thermal, mechanical, and electrical properties make it a promising dielectric material in electronics and communication industry.