The invention designs and builds up a new method for microscopic examination of escherichia coli and salmonella typhimurium based on germ growth. Through adding beta- lactam antibiotics in a to-be-tested sample solution, the germ is grown; film filtering and magnetic separation are combined so as to realize the specificity and high sensitivity detection of the escherichia coli and salmonella typhimurium, thus the germ number can be judged under an optical microscope; the method can be applied to a water sample; the whole detection process can be completed within 2 hours. The test verifies thatthe method can reduce the detection limit of escherichia coli and salmonella typhimurium to 5 cells and meet the requirement of fast detecting method. The method is simple in operation, low in cost and can be widely applied to the microscopic examination of the Gram negative bacteria in an actual sample.