A gas detecting device, comprising: a main body having a portable size defined by a length, a width and a height, and having a chamber, a first inlet, a second inlet and an outlet, wherein the chamber is formed within the main body, and the first inlet, the second inlet and the outlet are in fluid communication with the chamber; a particulate measuring module disposed within the chamber of the main body, and comprising an inlet channel, an outlet channel and a particulate detector, wherein the particulate detector is disposed within the particulate measuring module, the inlet channel is aligned with the second inlet of the main body, and the outlet channel is aligned with the outlet of the main body, wherein the gas can be introduced into the particulate measuring module through the inlet channel, a concentration of particulates in the gas can be measured by the particulate detector and the gas can be discharged from the outlet channel; and a control module configured to control actuations of a gas sensing module and the particulate measuring module, and convert detection results of the gas sensing module and the particulate measuring module into a monitoring value to be stored and transmitted to an external connection device for storage, characterized in that the gas detecting device comprises: the gas sensing module comprising a compartment body, a carrying plate, a sensor and an actuator, wherein the compartment body is located under the first inlet of the main body and has a partition plate disposed therein to divide an interior of the compartment body into a first compartment and a second compartment, and the partition plate has a notch for allowing the first compartment and the second compartment to be in fluid communication with each other, wherein the first compartment has an opening, the second compartment has an outlet aperture, the carrying plate is assembled on a bottom of the compartment body and is packaged on and electrically connected to the sensor, the sensor penetrates the opening and is disposed within the first compartment, the actuator is disposed within the second compartment, and the actuator and the sensor are separated from each other, wherein the actuator is actuated to introduce ambient gas into the gas sensing module through the first inlet, and the gas is measured by the sensor and discharged from the outlet of the compartment body. a main body having a portable size defined by a length, a width and a height, and having a chamber, a first inlet, a second inlet and an outlet, wherein the chamber is formed within the main body, and the first inlet, the second inlet and the outlet are in fluid communication with the chamber; a particulate measuring module disposed within the chamber of the main body, and comprising an inlet channel, an outlet channel and a particulate detector, wherein the particulate detector is disposed within the particulate measuring module, the inlet channel is aligned with the second inlet of the main body, and the outlet channel is aligned with the outlet of the main body, wherein the gas can be introduced into the particulate measuring module through the inlet channel, a concentration of particulates in the gas can be measured by the particulate detector and the gas can be discharged from the outlet channel; and a control module configured to control actuations of a gas sensing module and the particulate measuring module, and convert detection results of the gas sensing module and the particulate measuring module into a monitoring value to be stored and transmitted to an external connection device for storage, characterized in that the gas detecting device comprises: the gas sensing module comprising a compartment body, a carrying plate, a sensor and an actuator, wherein the compartment body is located under the first inlet of the main body and has a partition plate disposed therein to divide an interior of the compartment body into a first compartment and a second compartment, and the partition plate has a notch for allowing the first compartment and the second compartment to be in fluid communication with each other, wherein the first compartment has an opening, the second compartment has an outlet aperture, the carrying plate is assembled on a bottom of the compartment body and is packaged on and electrically connected to the sensor, the sensor penetrates the opening and is disposed within the first compartment, the actuator is disposed within the second compartment, and the actuator and the sensor are separated from each other, wherein the actuator is actuated to introduce ambient gas into the gas sensing module through the first inlet, and the gas is measured by the sensor and discharged from the outlet of the compartment body.