The utility model discloses a large constant-temperature reaction flow equalizing system and a heat exchanger. The reactor comprises a cylindrical reactor barrel, a reaction tube bundle is arranged inthe reactor barrel; an upper distribution plate and a lower distribution plate are respectively arranged at the upper end and the lower end of the reactor barrel; circulating holes are formed in theupper distribution plate and the lower distribution plate; upper tube plates are arranged above the upper distribution plate at intervals; lower tube plates are arranged below the lower distribution plate at intervals; two ends of the reaction tube bundle respectively penetrate through the upper distribution plate and the lower distribution plate and are fixed on the upper tube plate and the lowertube plate; an upper guide cylinder for enclosing the upper edge of the reactor cylinder in a sealing manner is connected between the upper tube plate and the upper part of the reactor cylinder; wherein a fluid outlet is formed in the upper guide cylinder, a lower guide cylinder for enclosing the lower edge of the reactor cylinder in a sealing manner is connected between the lower tube plate andthe lower part of the reactor cylinder, a fluid inlet is formed in the lower guide cylinder, and uniformly distributed inflow holes are formed in the wall surface of the cylinder between the lower edge of the reactor cylinder and the lower tube plate.