The evolution of hot image formation through medium with gain in consideration of the effect of spatialfilter is theoretically and numerically investigated. Based on the linear diffraction theory and small-scale self-focusing theory of Bespalov and Talanov, intensity distribution of hot image in conjugate planeis derived analytically. Then, the peak intensity of hot image for different medium gain and differentpinhole sizes are discussed in detail, the results show theoretical analysis is mostly approximate to thenumerical simulations, furthermore, it is found that suppressing effect on peak intensity ratio with smallgain coefficient is larger than that with bigger ones for determined pinhole size.