The thermal effect of sub-THz microchip dual frequency lasers (DFL) based on Nd:YVO4 crystals and its influence on the frequency difference of laser output signals are experimentally studied. In the experiment, the frequency difference tuning of laser signals is realized by tuning the DFL temperature. The experimental results indicate that, within a certain temperature range, the frequency difference of DFL signals linearly increases with the increment of temperature. Based on this point, one can realize the temperature tuning of frequency difference.