The strontium (5s2)1S0-(5s5p)3P1 intercombination transition is characterized far narrower natural line width than its counterpart dipode transition line (5s2)1S0-(5s5p)3P1 and has been applied in the field of optical frequency standards. In order to obtain its high quality spectrum, the line broadening factors of strontium (5s2)1S0-(5s5p)3P1 intercombination transition fluorescence spectrum are theoretically analyzed based on thermal atomic beam collimated by capillary tubes. The factors, including Doppler effect, laser line width, saturation broadening and transit-time broadening, are considered. Experimentally, the fluorescence spectrum including the saturated fluorescence spectrum, is obtained from the differently collimated strontium thermal atomic beams. The exprimental results show that the higher collimated thermal beam′s fluorescence spectrum line width is only 6.5 MHz, which is on the same order of magnitude as the Lamb-dip line width in the saturated fluorescence spectrum (1.7 MHz), and greatly reduces first-order Doppler broadening of spectra. And an external cavity diode laser is locked to the narrow line fluorescence spectrum by modulating the laser′s frequency directly, achieving a laser line width of about 0.72 MHz.