Details are given of an study of the characteristics of field-induced electron emission from hydrogen-free high $sp^3$ content(>90%) amorphous diamond (a-D) film deposited on heavily doped ($ ho$<0.01 $Omegacdot extrm{cm}$) n-type monocrystalline Si(111) substrate. It is demonstrated that a-D film has excellent electron field emission properties. Emission current can reach 0.9 $mu$A at applied field as low as 1 V/$mu extrm{m}$, and emission current density can be obtained about several mA/$ extrm{cm}^2$. The emission current is stable when the beginning current is at 50 $mu$A within 72 hours. Uniform fluorescence display of electron emission from whole face of the a-D film under the electric field of 10~20 V/$mu extrm{m}$ was also observed. It can be considered that the contribution of excellent electron emission property results from its smooth, uniform, amorphous surface and high $sp^3$ content of the a-D films.