Solar radiation received by a spaceborne near infrared laser altimeter prototype on orbit with various attitudes was analyzed based on the radiation theory. The working wavelength was 1064nm. With the system responsivity, the solar radiation reflected hy the star surface and received by the laser altimeter when it is working at the normal mode was discussed. And the background noise caused by this radiation was about ten times smaller than the system responsivity and its effect on the system can be neglected. According to the damage threshold of the APD, the solar radiation that directly irradiates the system was analyzed. And the duration of the APD to this radiation in space without any protection on it is 4s.