The invention discloses an on-line real-time analyzer provided with a multi-focus diffuse reflection optical collector, wherein the on-line real-time analyzer is internally provided with the multi-focus diffuse reflection optical collector, and the multi-focus diffuse reflection optical collector consists of a plurality of coaxial ring faces with continuous surfaces and discontinuous curvatures. The light which is collected by the multi-focus diffuse reflection optical collector and is projected on a photoelectric detector has less light intensity change range, the ratio of the maximum value of a light signal to the minimum value of the light signal is less than 2, and the ratio of the apparatus optical signal of the existing spherical optical collector is larger than 10. When collecting the diffuse reflection light in the process of dynamically measuring, the diffuse reflection optical collector can effectively solve the problem for affecting the account of the energy nonlinearity ofthe photoelectric detector caused by the larger change range of the light intensity. The each ring face of the multi-focus diffuse reflection optical collector has a coaxial turning face, is easily machined, has low manufacture cost, and is suitable for not only single experiment production but also mass production. The whole machine has simple structure and assembly, and effectively reduces the complex coefficient thereof.