A lamp projecting a starry sky, comprising: at least one beam generator; an interference filter, configured to produce a nebula effect; the beam generator is placed on a first side of the interference filter, a light beam generated by the beam generator irradiates onto the first side of the interference filter along an incident light path; at least one first lens, located on an emergent light path of the interference filter; the light beam emitted from the interference filter forms a moving and layering nebula projection after passing through the at least one first lens characterized in that a reflecting mirror is placed on a second side of the interference filter; after the interference filter is irradiated by the light beam, a light in the light beam passes through the interference filter after being subjected to 1) a reflection, or 2) a refraction, a reflection and a refraction in sequence, or 3) a refraction, multiple reflections and a refraction in sequence under action of the interference filter and the reflecting mirror; wherein the lamp projecting a starry sky comprises: a fixed cylinder and a first motor; wherein the interference filter is fixed at an opening at one end of the fixed cylinder, and the reflecting mirror is located between the interference filter and a slot bottom of the fixed cylinder, a power output shaft of the first motor is connected with the slot bottom; when the first motor runs, the fixed cylinder rotates to drive the interference filter and the reflecting mirror to rotate, or a connecting shaft connected with a first motor; wherein the first motor is connected to the interference filter through the connecting shaft, and the reflecting mirror is located on a side of the connecting shaft, a central axis of the reflecting mirror is parallel to the connecting shaft, when the first motor runs, the connecting shaft drives the interference filter to rotate, and the reflecting mirror stands still. at least one beam generator; an interference filter, configured to produce a nebula effect; the beam generator is placed on a first side of the interference filter, a light beam generated by the beam generator irradiates onto the first side of the interference filter along an incident light path; at least one first lens, located on an emergent light path of the interference filter; the light beam emitted from the interference filter forms a moving and layering nebula projection after passing through the at least one first lens characterized in that a reflecting mirror is placed on a second side of the interference filter; after the interference filter is irradiated by the light beam, a light in the light beam passes through the interference filter after being subjected to 1) a reflection, or 2) a refraction, a reflection and a refraction in sequence, or 3) a refraction, multiple reflections and a refraction in sequence under action of the interference filter and the reflecting mirror; wherein the lamp projecting a starry sky comprises: a fixed cylinder and a first motor; wherein the interference filter is fixed at an opening at one end of the fixed cylinder, and the reflecting mirror is located between the interference filter and a slot bottom of the fixed cylinder, a power output shaft of the first motor is connected with the slot bottom; when the first motor runs, the fixed cylinder rotates to drive the interference filter and the reflecting mirror to rotate, or a connecting shaft connected with a first motor; wherein the first motor is connected to the interference filter through the connecting shaft, and the reflecting mirror is located on a side of the connecting shaft, a central axis of the reflecting mirror is parallel to the connecting shaft, when the first motor runs, the connecting shaft drives the interference filter to rotate, and the reflecting mirror stands still. a fixed cylinder and a first motor; wherein the interference filter is fixed at an opening at one end of the fixed cylinder, and the reflecting mirror is located between the interference filter and a slot bottom of the fixed cylinder, a power output shaft of the first motor is connected with the slot bottom; when the first motor runs, the fixed cylinder rotates to drive the interference filter and the reflecting mirror to rotate, or a connecting shaft connected with a first motor; wherein the first motor is connected to the interference filter through the connecting shaft, and the reflecting mirror is located on a side of the connecting shaft, a central axis of the reflecting mirror is parallel to the connecting shaft, when the first motor runs, the connecting shaft drives the interference filter to rotate, and the reflecting mirror stands still.