This paper reports on an experiment for testing natural nuclear fusion at low temperature searching for evidence of the origin of 3He from natural nuclear fusion in deep Earth. The experiment was carried out using deuterium-loaded titanium foil samples and powder sample. Detection of charged particle was carried out using a low-level charged particle spectrometer. An Al foil was used as an energy absorber for identification of charged particle. Although the counting rate is very low in the experiment, the emission of energetic particle from the sample is observed and the particle is identified as a proton having energy about 2.8 MeV after exiting the titanium sample. This work provides a positive result for the emission of charged particle in the deuterium-loaded titanium foil samples at low temperature, but a negative result for the deuterium-loaded titanium powder sample. The average reaction yield is deduced to be (0.46±0.08) protons/h for the foil samples. With the suggestion that the proton originates from d-d reaction, we calculate the reaction rate for d-d reaction, and the obtained result is 1.4×10-24 fusion/d-d·sec. The negative result of the deuterium-loaded titanium powder sample suggests that the reaction yield might be correlated with the density or microscopic variables of deuterium-loaded titanium materials. The negative result also indicates that d-d reaction catalysed by μ-meson from cosmic ray can be excluded in the samples in this experiment. This paper reports on an experiment for testing natural nuclear fusion at low temperature searching for evidence of the origin of 3He from natural nuclear fusion in deep Earth. The experiment was carried out using deuterium-loaded titanium foil samples and powder sample. Detection of charged particle was carried out using a low-level charged particle spectrometer. An al foil was used as an energy absorber for identification of charged particle. This work provides a positive result for the emission of charged particles in the deuterium-loaded titanium foil samples at low temperature, but a negative result for the deuterium-loaded titanium powder sample. The average reaction yield is deduced to be (0.46 ± 0.08) protons / h for the foil samples. With the suggestion that the proton originates from dd reaction, we calculate the reaction rate for dd reaction, and the obtained result is 1.4 × 10-24 fusion / dd · sec. The negative result of the deuterium-loaded titanium powder sample suggests that the reaction yield might be correlated with the density or microscopic variables of deuterium-loaded titanium materials. The negative result also said that dd reaction catalysed by μ-meson from cosmic ray can be excluded in the samples in this experiment.