Based on the dual-wavelength high altitude detecting lidar we developed, daytime observation capability was realized in its sodium fluorescence channel by employing a Na (sodium) atomic filter and other relevant technologies. Because of the very narrow passband and very high out-of-band suppression of the Na atomic filter, the lidar echo at an 80-110 km altitude can be obtained even at noontime when background light from the sun is very strong. The capability for a 24-h continuous observation of the lidar system has been demonstrated by the preliminary observation result. This development makes the constant detection and investigation of high altitude atmosphere over the country possible.