In this paper, we present experimental study of effects of laser power and interaction length on collimation of chromium atomic beam by one-dimensional Doppler laser with large collimating slit of 5 mm in length, where the fluorescence is treated by Matlab. In addition, calculation by an adaptive step size, fourth-order Runge-Kutta type algorithm is done corresponding to the experiment. Both results show that with fixed interaction length, when the laser power becomes larger, or with fixed laser power, when the interaction length becomes longer, the FWHM of collimated atomic beam becomes smaller, and the peak becomes higher.