Currently, the ashing method is widely used to pretreat geo-electrochemical polyurethane foam samples. However, there may be volatilization loss of some elements such as Hg and As under high temperature. A geo-electrochemical exploration line in Luokedun hydrothermal lead-zinc polymetallic deposit in Inner Mongolia was selected as the research subject. A comparison of the exploration effects between the ashing method and microwave digestion in pretreating foam samples was made, and the contents of some related elements by High Resolution Inductively Coupled Plasma-Mass Spectrometry (HR-ICP-MS) and Atomic Fluorescence Spectrometry (AFS) were measured. Results are as follows, ①For more than ten elements including Zn, Cu, Fe, and La, abnormal patterns of the two methods were identical within uncertainty measurements and thus both methods can be used according to the work requirement. ②For Au and Pb, microwave digestion has serious problems related to homogeneity, representative and detection limit due to the small sample volume, making ashing the more suitable method. ③There is a significant loss in ashing for Hg, so microwave digestion is more suitable. ④For As, both analytical methods suffer a lot problems, therefore, dissolving the samples directly by nitric and perchloric acid using the pretreatment method for plant samples would be the preferable method.