The invention discloses a self-adjusting constant-micro-resistance check valve. The self-adjusting constant-micro-resistance check valve comprises a valve element plate, a valve element plate balance weight support, an upper balancing weight, a lower balancing weight, an inter-balancing-weight rotary shaft, a straight moving rail and an arc-shaped toothed rail, wherein the valve element plate is installed in a valve cavity through a rotary shaft and capable of in sealing with a valve inlet seal ring and can be opened and closed through rotation in the body of the valve cavity, the valve element plate balance weight support is connected with the end, provided with the rotary shaft, of the valve element plate, the upper balancing weight and the lower balancing weight are installed on the valve element plate balance weight support, the inter-balancing-weight rotary shaft is installed between the upper balancing weight and the lower balancing weight, the straight moving rail is installed on the lower side face of the upper balancing weight and is meshed with central teeth of the inter-balancing-weight rotary shaft, and the arc-shaped toothed rail is connected with end teeth of the inter-balancing-weight rotary shaft in a meshed mode. The self-adjusting constant-micro-resistance check valve is characterized in that an obtuse angle which is larger than 90 degrees is formed between the valve element plate balance weight support and the valve element plate when the check valve is installed horizontally, and an acute angle which is smaller than 90 degrees is formed between the valve element plate balance weight support and the valve element plate when the check valve is installed vertically; a valve element plate balance weight device is formed by the valve element plate balance weight support, the balancing weights installed on the valve element plate balance weight support, and a device which makes micro resistance be kept by the balancing weights when the valve element plate is opened by any degrees.