Presented is a convenient and timesaving design method for illuminating light being used as a pint-sized searchlight usually,based on white light emitting diode(LED) source. The process of design is studied mostly in advanced system analysis program(ASAP). The analyses on this kind of design method reveal the factors that would affect the luminous flux distribution of light, including the number of LED chips,the focus of reflecor and refractor, the corresponding position of reflector and refractor with the source. The zone cofficient method and point-by point method are discussed respectively to determine the LED source and the illuminace distribution of light.The desired parallel light output is gained after being optimized in ASAP at last.