The field emission characteristics of nano-diamond deposited on titanium substrate at various temperatures are studied. It was found that the emission current increases with increase of temperature and electric field，while the stability of the emission current basically does not change. The field emission characteristic deviates from classic Fowler-Nordheim theory. The mechanism of the emission current at different temperatures is analyzed. It may be due to the combined action of scale effect of the nano-diamond and masses of hot carrier produced by nano-diamonds in external electric field. In addition，the research indicates that larger current can be generated after titanium substrates being heated up to a certain degree in external electric field, which can have large effect on field emission，showing that the titanium substrate has a certain degree of temperature sensitivity and voltage sensitivity.