The present invention relates to a steam to carbon ratio control device including: a heat source, and an evaporation mixer and a steam separator interconnected by pipelines, said connecting pipelines of the evaporation mixer and the steam separator are provided with a temperature control device and a pressure control device, said evaporation mixer is provided with a natural gas inlet, a desalinated water inlet and a mixed gas outlet, the inlet of said heat source is connected with a end closer to the natural gas inlet of the evaporation mixer, the outlet of said heat source is connected to a end closer to the mixed gas outlet. Comparing with the prior art, the beneficial effect of the present invention is that it can accurately control the proportion of natural gas to steam and stably control the flow rates of natural gas and steam.