A securing and waterproof mechanism of a floodgate apparatus includes a pillar, a water retaining gate, a pair of retaining bases and a securing member. The pillar has a retaining groove for receiving the water retaining gate. The retaining bases are attached to two opposite sides of the pillar. Each retaining base has at least one vertical channel. The securing member has two hook portions at one side. Each hook portion has a horizontal bar and a vertical bar extending upward from a distal end of the horizontal bar. Under this arrangement, the vertical bar of each hook portion is fitted in the vertical channel of the respective retaining base to prevent the securing member from sliding horizontally off the respective retaining base.