Based on the gas kinetic theory, the general analytical expression for the drag force on non-spherical particles is obtained in the present paper. This model is applicable to rigid convex non-spherical particle suspending in a diluted gas, wherein multiple collisions between the gas molecules and the particle are ignored. Based on the Maxwellian scattering model, i.e., specular and diffusion collisions between gas molecule and the particle, the general analytical expression for the drag force on particles can be derived by evaluate the momentum transfer upon gas-particle collisions. For several common non-spherical particles, such as spheres, cylinders, ellipsoids and cones, the expressions for drag force are also obtained. It is found that the drag force on non-spherical particles depends on the geometric shape and orientation. In the free molecular regime, the particle is expected to undergo a rapidly rotation in the case of weak potential field, which induces a uniformly random distribution of the paricle orientation. Then, the expression of the orientation-averaged drag force on non-spherical particles can be derived, which is found to be proportional to the surface area of the particle, and the proportion coefficient is independent of the particle size or shape. The findings in the present paper can be employed to simplify the calculation of the drag forces on non-spherical particles in the free molecular regime.