A virtual image display system , comprising: a handheld electronic device , having a first battery ; and a virtual image display , coupled to the handheld electronic device and having a second battery , wherein the handheld electronic device is configured to: calculate (S201) a power supply time of the first battery ; calculate (S202) an expected discharge time of the second battery under a discharge condition; compare (S203) the power supply time and the expected discharge time to generate a comparison result; and adjust (S204) a supply current provided by the handheld electronic device to the virtual image display according to the comparison result; wherein when the comparison result indicates that the power supply time is less than the expected discharge time (S302), the handheld electronic device is configured to activate (S305) a power saving mechanism of the handheld electronic device to reduce a power consumption of the handheld electronic device , wherein the power saving mechanism of the handheld electronic device comprises at least one of reducing a brightness of a screen backlight of the handheld electronic device ; reducing an antenna emission performance of the handheld electronic device ; and reducing a working clock of the handheld electronic device . a handheld electronic device , having a first battery ; and a virtual image display , coupled to the handheld electronic device and having a second battery , wherein the handheld electronic device is configured to: calculate (S201) a power supply time of the first battery ; calculate (S202) an expected discharge time of the second battery under a discharge condition; compare (S203) the power supply time and the expected discharge time to generate a comparison result; and adjust (S204) a supply current provided by the handheld electronic device to the virtual image display according to the comparison result; wherein when the comparison result indicates that the power supply time is less than the expected discharge time (S302), the handheld electronic device is configured to activate (S305) a power saving mechanism of the handheld electronic device to reduce a power consumption of the handheld electronic device , wherein the power saving mechanism of the handheld electronic device comprises at least one of reducing a brightness of a screen backlight of the handheld electronic device ; reducing an antenna emission performance of the handheld electronic device ; and reducing a working clock of the handheld electronic device . calculate (S201) a power supply time of the first battery ; calculate (S202) an expected discharge time of the second battery under a discharge condition; compare (S203) the power supply time and the expected discharge time to generate a comparison result; and adjust (S204) a supply current provided by the handheld electronic device to the virtual image display according to the comparison result; wherein when the comparison result indicates that the power supply time is less than the expected discharge time (S302), the handheld electronic device is configured to activate (S305) a power saving mechanism of the handheld electronic device to reduce a power consumption of the handheld electronic device , wherein the power saving mechanism of the handheld electronic device comprises at least one of reducing a brightness of a screen backlight of the handheld electronic device ; reducing an antenna emission performance of the handheld electronic device ; and reducing a working clock of the handheld electronic device . <EOS>