A novel means of lens focal length measurement was proposed based on Hartmann-Shack principle of wavefront detection. Mathematical approaches of focal length measurement were deduced. In the experiments, laser sources with wavelength of 633 nm and 780 nm were separately used and focal length of three pieces of doublets were measured by the two wavelengths.The results show that the measured result can truly reflect the designed focal length by using 633 nm wavelength laser beam, which indicates that this measurement method is feasible and reliable. Meanwhile, the measured result by using 780 nm wavelength laser beam shows larger differences compared with its 633 nm counterpart, which reveals that this method can also be used to evaluate residual spherical aberrations, chromatic aberrations and manufacturing tolerance.