An illumination system, comprising: a light source , adapted to emit a light beam (B); at least one light-diffusion element , disposed on a transmission path (P) of the light beam (B) from the light source , wherein the at least one light-diffusion element and a reference plane (RF) perpendicular to the transmission path (P) of the light beam (B) from the light source have an inclined angle therebetween, so that the at least one light-diffusion element is inclined to the transmission path (P) of the light beam (B) from the light source ; a wavelength conversion module , disposed on a transmission path (P) of the light beam (B) from the at least one light-diffusion element , wherein a long axis direction of a light spot (BP) projected on the wavelength conversion module is perpendicular to an extending direction of a boundary between the reference plane (RF) and the at least one light-diffusion element , the wavelength conversion module is adapted to convert a first portion (B1) of the light beam from the at least one light-diffusion element to a converted light beam (C), and the converted light beam (C) and a second portion (B2) of the light beam (B) from the at least one light-diffusion element form an illumination light beam (IB); and a light-homogenizing element , disposed on a transmission path (P) of the illumination light beam (IB), wherein a shape of a light-input end (X1) of the light-homogenizing element is a rectangle having a pair of long sides and a pair of short sides, and wherein the long sides of the light-input end (X1) correspond to the long axis direction of the light spot (BP) projected on the wavelength conversion module . a light source , adapted to emit a light beam (B); at least one light-diffusion element , disposed on a transmission path (P) of the light beam (B) from the light source , wherein the at least one light-diffusion element and a reference plane (RF) perpendicular to the transmission path (P) of the light beam (B) from the light source have an inclined angle therebetween, so that the at least one light-diffusion element is inclined to the transmission path (P) of the light beam (B) from the light source ; a wavelength conversion module , disposed on a transmission path (P) of the light beam (B) from the at least one light-diffusion element , wherein a long axis direction of a light spot (BP) projected on the wavelength conversion module is perpendicular to an extending direction of a boundary between the reference plane (RF) and the at least one light-diffusion element , the wavelength conversion module is adapted to convert a first portion (B1) of the light beam from the at least one light-diffusion element to a converted light beam (C), and the converted light beam (C) and a second portion (B2) of the light beam (B) from the at least one light-diffusion element form an illumination light beam (IB); and a light-homogenizing element , disposed on a transmission path (P) of the illumination light beam (IB), wherein a shape of a light-input end (X1) of the light-homogenizing element is a rectangle having a pair of long sides and a pair of short sides, and wherein the long sides of the light-input end (X1) correspond to the long axis direction of the light spot (BP) projected on the wavelength conversion module . <EOS>