Image sharpness evaluation function is the core of Depth from Focus (DFF) method for 3D profile measurement. Crucially, the accuracy of depth measurement is determined by the evaluation function. An image sharpness evaluation function using high-frequency component variance weighted entropy was proposed. The quantitative indicators including the resolution ratio and the sensitivity factor were used to test the proposed function and the common functions. The comparative data showed that the proposed function could achieve better focusing performance than the other functions. The focusing position in depth direction could be precisely confirmed by implementing the Gaussian fitting to the image sharpness curve calculated through the proposed function. Focusing repeatability and standard step height measurement were tested. The standard deviation of the data of the focusing repeatability experiment was 2.82 μm. And the standard deviation of the measurement height of the standard step was 12 μm. The result verifies the feasibility of the proposed method for high precision non-contact 3D measurement.