To satisfy the demand for multimode lasers source in chaos applications, the multimode output of a Fabry-Perot laser is used as the seed laser, and the nonlinear characteristics of an optoelectronic oscillation loop is used to generate multimode chaotic lasers in this study. Experimental results indicate that, compared with the conventional optoelectronic oscillation loop for generating chaotic laser, this scheme reduces the required loop gain by 3 dB, increases the full power spectra bandwidth by 3.3 GHz, and decreases the time-delay signature by approximately 80% while generating multimode chaotic lasers. Additionally, each mode exhibits broad and flat power spectra, and the correlation between modes significantly decreases as the mode spacing increases. This paper presents a new method for generating multimode chaos lasers.