The work aims to study the effect of carbon nanotubes on the electrothermal properties of carbon-based water-based conductive ink, so as to find the heating ink with the best content of carbon nanotubes. The single factor method was adopted to prepare several groups of carbon-based water-based electrothermal inks by adding different contents of carbon nanotubes to the original carbon-based water-based conductive ink. Through tests on SEM, TEM, electrothermal power, contact angle, etc., the optimal preparation formula of carbon-based water-based electrothermal ink was explored. The heating temperature and electric power of carbon-based water-based electrothermal inks with different carbon nanotube contents were different. Under certain other conditions, with the increase of carbon nanotube content, the electrical and thermal conductivity of carbon-based water-based conductive ink firstly decreased and then increased. When the mass fraction of carbon nanotubes was 0.75%, the carbon-based water-based conductive ink reached the highest temperature (147 °C), and the power was relatively low (4.4 W), which was the formulation of the carbon-based water-based electrothermal ink with the best conductivity. Adding an appropriate amount of carbon nanotubes to the conductive ink can improve the heating performance of the ink.