Line detection is one of the most long-lasting problems in image processing. In this paper, we address the problem of detecting strong/weak lines and long/short lines in gray level images simultaneously. Our technique consists of three steps: image gradient enhancement, modified Hough Transform (HT) and line fitting. The gradient direction is fully exploited in our technique, which provides additional cues for weak line detection. Experiments on various images are presented to verify our approach. The results show that our technique has a superior detection rate than conventional HT algorithm, especially for short and weak lines.