This invention relates to a method for producing Al-Ti alloy by electrolytic coprecipitation. The method comprises: feeding TiO2 into an electrolytic bath from the feeding mouth 3-5 times each day, samplying and analyzing after 2-3 h, discharging Al, terminating TiO2 feeding to lower the content of Ti in the electrolytic bath when electrolytic coprecipitation is performed for 4-6 months, feeding TiO2 into another electrolytic bath, and controlling the content increase of TiO2 in the electrolytic bath match the content decrease of TiO2 in the first electrolytic bath to guarantee the supply of Al-Ti alloy. By the method, the electrolytic baths have stable running and no obvious decrease of current efficiency; the furnace bottom is protected. The method can be applied to 300 kA electrolytic bath stably and permanently.