The utility model provides a rainwater is collected and is utilized device for big -arch shelter is irrigated, including water storage box, medicinal water tank and pure water tank, be equipped with on the water storage box and hold in the palm the shoulder, ask the shoulder -mounted to be equipped with mesh partition, the water storage box divide into and sinks mud room and reservoir chamber, sink the slope of mud room bottom, sink mud room lower part to be equipped with water pipe, water pipe one end extends to the below reservoir chamber, the last floater that is equipped with of water pipe, the floater passes through the rope with the water pipe inner wall and links to each other, the reservoir chamber below is equipped with the raceway, medicinal water tank body is equipped with the fluviograph outward, and medicinal water tank bottom is equipped with the agitator, is equipped with the mouth of dosing on the medicinal water tank lateral wall, the inside filter layer that is equipped with of pure water tank. The utility model discloses can deposit the silt in the rainwater to shunt according to the usage difference, the crop liquid medicine can be regarded as to the rainwater in the medicinal water tank, prevents the insect pest, and the rainwater among the pure water tank can be used for wasing fruit vegetables etc. Can make full use of to the rainwater.