SPF and PA index present the resistance ability of sunscreen to UVA (Ultraviolet A) and UVB (Ultraviolet B) respectively. The present article focuses on the research on the relationship between ultraviolet transmittance and sunscreen ability based on definition of sunscreen efficiency and a simple and significant result was obtained by deducing. The technique we applied is spectral analysis dealing with ethanol-ethyl ether mixed solvent by ultraviolet and visible light spectrophotometer. We measured the UVA and UVB transmittance of 69 common sunscreen samples. The measurement result shows that spectral analysis method could differentiate sunscreens with different SPF and PA and identify whether the parameter value marked is accurate. So, an effective method is provided for the measurement of SPF and PA value. If different types of ultraviolet absorbent or UV scattering dose is added in sunscreen, the authors can distinguish them easily through the shape of the transmittance curve. In our sunscreen samples measured, domestic brands and imported brands are classified into two categories. By comparing the experimental results, the authors found that the domestic sunscreen and import sunscreen have no significant difference in sun block efficiency as long as the authors adopt the product of qualified manufacturer.