Embodiments of the disclosure provide a projector including a housing, a light source module, a light engine module, a projection lens module, and a thermal module. An airflow is formed in the housing. The thermal module is disposed in the housing and includes a base and a plurality of fins. The housing has a space for accommodating the thermal module, and a dimension of the space is L. An average velocity of the airflow before entering the plurality of fins is V, and a pitch between adjacent fins of the plurality of fins is P, and a reference value Y=[2.9*(V+1)*(P−2.3)∧2+2.4*(V−3.308)∧2+15.82], and when L is greater than or equal to Y, the thermal module is a three-dimensional vapor chamber thermal module or a tower thermal module.