The invention mainly relates to an automatic rainwater collecting and purifying tool and a rainwater collecting and purifying method. The automatic rainwater collecting and purifying tool comprises abottom plate, a guiding and cleaning device is mounted at the front end of the bottom plate, and a particle filtering device is mounted at the lower end of the guiding and cleaning device. A purifyingand water introducing pipe is mounted on the lower side of the rear end of the particle filtering device, the lower end of the purifying and water introducing pipe is connected with a water purifyingtank, the water purifying tank is mounted on the bottom plate, and a water outlet valve is arranged on the water purifying tank. According to the automatic rainwater collecting and purifying tool andthe rainwater collecting and purifying method, the problems that in an existing roof rainwater treatment and purification process, rainwater on a roof cannot be directly collected, the rainwater flowing to the ground needs to be manually guided and collected uniformly, dry branches and fallen leaves in the rainwater need to be cleared up manually through a fishing tool, the rainwater needs to stand still, particles in the rainwater precipitate, the rainwater on the ground is guided and collected uniformly, debris in the rainwater is increased, the manual fishing intensity is large, long timeis spent, and the work efficiency is low can be solved.