It makes sense to understand the exploration and development of marine resources and oil-gas investment environment in countries along “the 21stcentury maritime silk road” for choosing potential cooperation countries in marine geological survey and investment with the purpose of decreasing exploration and investment risks. This paper uses the revised G1 method by standard deviation to set up an evaluation index system composed of 10 tier-1 indexes and 58 tier-2 indexes, which is used to analyze the 15 southeastern and southern Asian countries. Results show that those on top are India, Indonesia and Malaysia in general scores, India in marine resources and exploration, Singapore in political and social environment, Indonesia in oil-gas evaluation, and Burma showing an outstanding aspect in openness and cooperation. In light of the latest international diplomatic situation and cooperation, Burma, Pakistan, Cambodia, Malaysia and Singapore are key nations in marine resources exploration and oil-gas investment, and Indonesia, Brunei, Thailand, East Timor, Bangladesh have good basis or prospects for cooperation.