Multipath error is one of the last obstacles for GNSS performance improvement, and accordingly multipath mitigation techniques are developed rapidly. However, there is a lack of evaluation rules for the multipath mitigation performance. Three evaluation criteria based on the multipath error envelope were proposed; the multipath error formulae for both ELS technique and Double-delta technique were derived for the first time; hence calculation expressions of the multipath mitigation performance evaluation for the above two techniques and narrow correlator technique were presented. This research can be used as a guideline for the parameter design of multipath mitigation techniques in GNSS receiver.