To increase wavefront detecting speed of the wavefront sensor, a new computing-free method based on holography is researched. With thin hologram approximation, we get the numerical model based on the fast Fourier transform (FFT) algorithm and the first 8 order Zernike aberrations are detected by holographic wavefront sensor under this numerical model. The root-mean-square (RMS) value of detection error is 0.24 rad. An experimental device is set up to validate the numerical simulation in our laboratory and the RMS value of detection error is 0.29 rad. The experimental results indicate that the computing-free wavefront sensing method based on holography can detect the low order Zernike aberrations with high efficiency.